The determination method of salt content in soy sauce is described as“Measurement of Salt Content”in JAS (Japanese Agriculture Standard). Potentiometric titration and Mohr method is defined in JAS as determination method of salt content, potentiometric titration is more common method because of its ease and high precision. The sample is acidified by nitric acid and the concentration of salt is determined byprecipitation titration with silver nitrate titrant using the silver electrode. NaCl ＋ AgNO₃ → AgCl ＋ NaNO₃
An example of successive determination of concentration of acid and salt chloride in dressing is introduced here. Acid and salt are determined as acid and sodium chloride.
At first, titration of acetic acid with sodium hydroxide titrant is performed. Next, the sample solution is acidified by adding nitric acid, then titration of sodium chloride is performed with silver nitrate titrant.
* The titration for sodium chloride with silver nitrate has to be performed under acidic condition using nitric acid.
Example of sequential titration for vitamin C and citric acid in a soft drink is introduced here.
(1) Firstly, perform neutralization titration for citric acid with sodium hydroxide standard solution.
(2) After the titration, add acetic acid to adjust to acidic pH. Perform redox titration for vitamin C (ascorbic acid) by iodine standard solution.
The sequential titration of citric acid and vitamin C will be possible by additional option (buret and simplified dispenser).
Successive measurement of acid (citric acid) and amino nitrogen in grapefruit juice and its titration process will be introduced.
The amino nitrogen.is determined by Formol method which is simplified method of Van Slyke method. Firstly, measure the acid (citric acid) in sample solution by the titration with sodium hydroxide standard solution until the pH reaches 8.1 as described in the formula (1). After that, add sodium hydroxide standard solution to adjust the pH to 8.4. Add neutral buffered formalin solution to react amino nitrogen with formalin for generating carboxylic acid (formula (2)). Titrate the carboxylic acid with sodium hydroxide until the pH reaches 8.4, and measure amino nitrogen based on formula (3).
Acid value of oils and fats is defined as “amount (mg) of potassium hydroxide required to neutralize fatty acid in 1 g of sample” (Formula (1)). R-COOH + KOH → R-COOK + H₂O ・・・(1)
It is used for evaluation of free fatty acid content as quality index of oils and fats. This method is described in a variety of official standards such as “Japan Agricultural Standards” and Pharmacopoeias. Example of titration for acid value in cooking oil is introduced here.
Reference
1) Japanese Pharmacopoeia Seventeenth Edition
Fatty acid in cooking oil, for example, oleic acid and linoleic acid absorb one or two of iodine molecules. Other kinds of cooking oils also absorb specific amount of iodine.
Iodine value means the “g” value of halogen which adhere to 100 g of sample; it is defined as indicators for unsaturated bond components of oils and fat in Pharmacopoeias: JP, USP, and EP.
There are two kinds of measuring methods such as Hanus method and Wijs method for Iodine value measurement. The former uses iodine bromide and the latter uses iodine chloride as halogen. In this chapter, the measurement example using more popular Wijs method is introduced.
Excess ICl in regard to the number of double bond is added on Wijs method. One halogen molecule binds to double bond of oils and fat as the following formula (1). ･･･(1)
The Iodine value is determined by excessively-remained ICl which is titrated with sodium thiosulfate according to the following formula (2). 2Na₂S₂O₃ ＋ ICl → Na₂S₄O₆ ＋ NaI ＋ NaCl･･･(2)
When potassium hydroxide ethanolic solution is added to fats and oils and heated, glyceride produces fatty acid potassium salt and glycerin by saponification (Formula (1)), and free fatty acid produces fatty acid potassium salt and water (Formula (2)). RCOOR′ ＋ KOH → RCOOK ＋ R′OH・・・(1) RCOOH ＋ KOH → RCOOK ＋ H₂O・・・(2)
Saponification value is defined as “amount (mg) of potassium hydroxide required to react with heating in 1 g of fats and oils sample”. This method is described in a variety of official standards such as “Japan Agricultural Standards” and Pharmacopoeias. Example of titration for saponification value in cooking oil is introduced here.
Reference
1) Japanese Pharmacopoeia Seventeenth Edition
Degraded fats and oils include peroxide chemical species. Therefore, determination of peroxide value is an effective analytical method to know the index of fat and oil degradation. This method is described in a variety of official standards such as Pharmacopoeias: JP, USP, and EP.
Definition of peroxide value depends on respective standard method. For example, it is expressed as “amount of active oxygen in 1 kg of sample [mg/kg]” in Pharmacopoeias. Active oxygen can oxidize potassium iodide to iodine (Formula (1)). “Method of Analysis in Health Science” in Japan defines peroxide value as “milliequivalents of iodine generated from potassium iodide in 1 kg of sample [meq/kg]”. Each titration are performed in a same procedure even if the expressions on definitions are different between these standard methods; generated iodine is finally titrated with sodium thiosulfate (Formula (2)).
Example of titration for peroxide value in cooking oil is introduced here. Experimental procedure is implemented in relation to “Methods of Analysis in Health Science” in Japan.
R－OOH ＋ 2I⁻ ＋ 2H⁺ → R－OH ＋ I₂ ＋ H₂O・・・(1) I₂ ＋ 2Na₂S₂O₃ → 2NaI ＋ Na₂S₄O₆・・・(2)
An example for acid value measurement of orange juice performed by neutralization titration is introduced here.
Dispense the sample and add pure water. Titrate with sodium hydroxide standard solution until the pH reaches 8.1 using a glass electrode (neutralization titration). Acid value is calculated by the standard solution volume titrated until the pH reaches 8.1 as the citric acid content.
Reaction between citric acid and sodium hydroxide is described by the following formula (1).
･･･(1)
Many soft drinks contain vitamin C (ascorbic acid). Vitamin C is included as not only nutrient factor but also an antioxidant for drinks. There are iodine titration method and indophenol method for analysis of vitamin C, this report introduces indophenol method.
Firstly, acidify the sample with mixed solution of metaphosphoric acid and acetic acid. After that, titrate with indophenol standard solution. The endpoint of the titration is detected as color change from colorless to red-purple with photometric probe.
Sodium acetate is widely used in chemical and medical industry (E.g. Buffer, Antifreezing agent, Alkalizing supplements, Dye chemical, Hydragogue). Determination method of sodium acetate is described on Japanese Pharmacopoeia and Japanese Industrial Standard (JIS K8371). Both methods employ perchloric acid titration method, dissolve the sample in glacial acetic acid and titrate with perchloric acid – acetic acid standard solution. Endpoint is detected by potentiometric titration with glass / reference electrodes. CH₃COONa ＋ HClO₄ → CH₃COOH ＋ NaClO₄
Determination method of available iodine in mouthwash containing povidone-iodine which is described in Japanese Pharmacopoeia is introduced here.
Dispense the sample and dilute it with DI water. Redox titration with sodium thiosulfate is performed based on the following formula (1). I₂ ＋ 2Na₂S₂O₃ → 2NaI ＋ Na₂S₄O₆・・・(1)
This report introduces an example of measurement for sodium chloride in peritoneal dialysis solution with precipitation titration. The sample is acidified by nitric acid and the concentration of sodium chloride is determined by precipitation titration with silver nitrate titrant using the silver / reference electrode. NaCl ＋ AgNO₃ → AgCl ＋ NaNO₃
Determination for papaverine hydrochloride is defined in Japanese Pharmacopoeia. Papaverine hydrochloride is used for improvement of vasodilatation and symptoms on gastritis, disease of biliary tract (gallbladder) system, acute arterial embolus, acute pulmonary embolism, peripheral circulatory failure, and inadequate coronary circulation.
The purity determination of papaverine hydrochloride using potentiometric titration with perchloric acid titrant is introduced in this report. Sample is dissolved by heating with acetic anhydride / glacial acetic acid mixture and cooled to room temperature. After that, the titration is performed, 1 mol papaverine hydrochloride reacts with 1 mol perchloric acid quantitatively. Papaverine hydrochloride (C₂₀H₂₁NO₄・HCl, FW:375.85)
Measurement method with perchloric acid – acetic acid standard solution is defined as a quantitative determination method for each drug and medicine in Japanese Pharmacopoeia. Standardization of perchloric acid – acetic acid standard solution with potassium hydrogen phthalate is also described there. This report introduces the standardization procedure that potassium hydrogen phthalate is dissolved in acetic acid, then it is titrated with perchloric acid – acetic acid standard solution. The factor of perchloric acid – acetic acid standard solution is determined with potentiometric titration. 1 mol potassium hydrogen phthalate reacts with 1 mol perchloric acid quantitatively on this titration (formula 1). ･･･(1)
Sodium citrate is used as anticaking agent for blood in pharmaceutical field. Quantitative determination method for sodium citrate is stipulated in Japanese Pharmacopoeia.
This report introduces an example of potentiometric titration for sodium citrate that well-dried sample is dissolved in acetic acid, then it is titrated with perchloric acid – acetic acid standard solution. C₆H₅Na₃O₇ ＋ 3HClO₄ → C₆H₈O₇ ＋ 3NaClO₄
The determination method of anion surfactant uses a cation surfactant with an oppos ite charge as the titrant. The end point is the point at which the charge becomes neutral due to the reaction between the anion and the cation. Benzethonium chloride is used as the cation standard solution.
This report introduces an example of determinati on of anion surfactant sodium alkylbenzene sulfonate in detergent by potentiometric titration using a surfactant electrode as an indicator electrode.
The precipitation titration using lead ion-selective electrode achieves the measurement of sulfate ions. Lead sulfate is generated by adding lead nitrate to sulfate ion. The potential reading with lead ion-selective electrode differs depending on the concentration of sulfate ion in sample solution. The maximum change in potential is observed when it reaches the equivalent point of sulfate and lead ions. The concentration of sulfate ion is determined by the titrant volume consumed until it reaches the inflection point.med until it reaches the inflection point. SO₄²- ＋ Pb(NO₃)₂ → PbSO₄ ＋ 2NO₃-
This report introduces an example of the measurement for sulfate ion in bath additive with using lead ion-selective electrode.
The determination method of anion surfactant uses a cation surfactant, with an opposite charge, as the titrant. The end point is the point at which the charge becomes neutral due to the reaction between the anion and the cation. Benzethonium chloride is used as the cation standard solution.
This report introduces a method for standardization of benzethonium chloride standard solution. Sodium dodecyl sulfate is used for standard solution. First, determine the purity of sodium dodecyl sulfate. Add diluted sulfuric acid to sodium dodecyl sulfate, heat to reflux, and then titrate with sodium hydroxide standard solution.
Subsequently, prepare the standard solution of sodium dodecyl sulfate whose purity has been determined, and standardize the benzethonium chloride standard solution with titration against sodium dodecyl sulfate standard solution.
Quantitative determination for chloride ions in tap water is stipulated in Standard Methods for the Examination of Water, and Standard Methods of Analysis for Hygienic Chemists, etc. A small amount of chloride ion is contained in natural water, it is said to increase due to contamination of domestic drainage, industrial drainage, and farming drainage, etc. Standard Methods for the Examination of Water adopts ion exchange chromatograph method and Mohr method (titration method) as the chloride quantitative determination method. The detection limit for ion exchange chromatograph method is 0.2 mg/L. Mohr method is generally applied for samples including chloride ions in mg/L or more. This report introduces the Mohr method with precipitation titration, which quantifies chlorides by potentiometric titration with silver indicator electrode instead of the color indicator titration described in Standard Methods for the Examination of Water.
100 mL of the sample water is collected and acidified with nitric acid for potentiometric titration with silver nitrate titrant. Cl⁻ + AgNO₃ → AgCl↓ + NO₃⁻
Hardness in water is total amount of calcium and magnesium ion in water converted to mg/L of comparable calcium carbonate. “Hardness” has the following types:
(1) Total hardness Total amount of calcium and magnesium ions
(2) Calcium hardness Calcium ion
(3) Magnesium hardness (Total hardness) – (Calcium hardness)
(4) Non-carbonate hardness (Permanent hardness)
(5) Carbonate hardness (Temporary hardness)
These are stipulated in some applicable standard such as Standard Methods for the Examination of Water, Standard Methods of Analysis for Hygienic Chemists, and JIS K0101 Testing methods for industrial water etc.
This report introduces an example for determination of total hardness in tap water with photometric titration method using EDTA standard solution according to the Standard Methods for the Examination of Water.
Take 100 mL of sample and add 1 mL of 0.01 mol/L magnesium chloride, 2 mL ammonia buffer, and 0.2 mL of EBT indicator. Titrate with 0.01 mol/L EDTA standard solution (red →blue color). Perform the same procedure for 100 mL of DI water instead of sample as blank measurement. CaCO₃ + Na₂EDTA → Ca-EDTA + Na₂CO₃ MgCO₃ + Na₂EDTA → Mg-EDTA + Na₂CO₃
There are determination methods for hardness in tap water as follows: (1) Total hardness defined as the sum of calcium and magnesium ion converted to mg/L as calcium carbonate (CaCO3), (2) Calcium hardness determined by calcium ion concentration.
The measurement method for calcium hardness is similar to that of total hardness. Adjust the pH of sample water to higher than pH 12 with sodium hydroxide to mask the reaction of magnesium and EDTA. Start titration with 2-hydroxy-1-(2-hydroxy-4-sulfo-1-naphthylazo)-3-naphthoic acid (NN) indicator. Its color changes from red to blue. CaCO₃ + Na₂EDTA → CaEDTA + Na₂CO₃ This report introduces an example of calcium hardness measurement for tap water with photometric titration method using EDTA standard solution according to the Standard Methods for the Examination of Water.
Tap water chlorinated from lake water and river water contains residual chlorine. The residual chlorine is sometimes called available chlorine, which is composed of free residual chlorine and combined residual chlorine.
Standard Methods for the Examination of Water adopts the following methods as determination method for residual chlorine.
・Dimethyl -p- phenylenediamine (DPD) method ………………………………………………Colorimetric method
・Dimethyl -p- phenylenediamine (DPD) titration method………………………………………Titration method
・Amperometric titration method (Titration method with phenylarsenoxide solution) ………Titration method
・Iodometric titration method………………………………………………………………………Titration method
This report introduces an example for determination of residual chlorine in tap water with iodometric titration method.
Residual chlorine oxidizes potassium iodide in acidic solution to generate free iodine. Cl₂ + 2I⁻ → I₂ + 2Cl⁻
The generate iodine is potentiometrically titrated with sodium thiosulfate standard solution. I₂ + 2Na₂S₂O₃ → 2NaI + Na₂S₄O₆
ASTM D1253 : Standard Test Method for Residual Chlorine in Water
Natural water contains alkaline components such as hydroxides and carbonates. Such water indicates alkaline pH, the alkalinity is used as an index. The alkalinity is expressed as mg/L of calcium carbonate (CaCO₃) equivalent for these alkaline components. Alkalinity is divided into phenolphthalein alkalinity (P alkalinity) and total alkalinity (T alkalinity or M alkalinity) by the pH value of neutralization point.
Total amount of the hydroxides and half amount of carbonates are measured when it is titrated to about pH 8.3 with sulfuric acid titrant. 2OH⁻ + H₂SO₄ → SO₄²⁻ + 2H₂O 2CO₃²⁻ + H₂SO₄ → SO₄²⁻ + 2HCO₃⁻
All of the bicarbonates are neutralized when it is titrated successively to about pH 4.8. HCO₃⁻ + H₂SO₄ → SO₄²⁻ + 2CO₂ + H₂O
This report introduces a measurement example for bottled water using potentiometric titration as end point detection method according to Standard Methods for the Examination of Water.
The control and analysis of nickel plating solution are very important process for the product quality. Analytical components of the general nickel plating solution are 1) nickel sulfate, 2) nickel chloride, and 3) boric acid. This report introduces an example of measurement for nickel chloride in nickel plating solution determined by potentiometric titration with silver nitrate standard solution. NiCl₂ + 2AgNO₃ → Ni (NO₃)₂ + 2AgCl
The control and analysis of chromium plating solution are very important process for the product quality. General analytical components of the chromium plating solution are the following 5 components.
(1) Chromic anhydride (CrO₃)
(2) Chromium (III) (Cr³⁺)
(3) Sulfuric acid
(4) Fluoride ion
(5) Iron
This report introduces an example of measurement for (1) chromic anhydride and (2) chromium (III).
The measurement procedure of chromic anhydride is as follows: Take diluted sample solution and add sulfuric acid to acidify it. Accurately add a certain amount of ammonium iron (II) sulfate in an amount sufficient to react the entire amount of chromic anhydride, and react the chromic anhydride by the reaction formula (1). The unreacted ammonium iron (II) sulfate is titrated with a potassium permanganate standard solution according to reaction formula (2) to obtain chromic anhydride.
The measurement procedure of chromium (III) is as follows: Take diluted sample solution and add sodium hydroxide to adjust it to pH 12 or more. Add hydrogen peroxide to oxidize chromium (III) to chromium (VI). Boil off and degrade the excess hydrogen peroxide by the reaction formula (3). Add sulfuric acid to acidify it. Accurately add a certain amount of ammonium iron (II) sulfate in an amount sufficient to react the entire amount of chromium (VI), and react the chromium (VI) by the reaction formula (1). The unreacted ammonium iron (II) sulfate is titrated with a potassium permanganate standard solution according to reaction formula (2) to obtain total chromium amount in term of chromic anhydride. Chromium (III) is obtained by subtracting chromic anhydride from total chromium amount.
Tin (Sn²⁺) in solder plating solution is determined by redox titration with iodine. Solder plating solution contains Sn (II) ions, Sn (IV) ions, and acids etc. Iodine works as oxidizing agent for stannous ion. Sn (II) ions are readily oxidized by oxygen in the air to be Sn (IV) ions. The measurement environment under carbon dioxide or nitrogen gas could provide reliable results. Sn²⁺ ＋ I₂ → Sn⁴⁺ ＋ 2I⁻
This report introduces a measurement example that sample is added to solution under carbon dioxide gas generated by the decomposition of sodium hydrogen carbonate, and titrated with iodine titrant.
Sulfuric acid and hydrogen peroxide are main components of the etching solution which is used for cleaning the copper surface (soft etching) or half etching. The concentration of sulfuric acid and hydrogen peroxide have to be properly controlled to maintain constant etching speed because hydrogen peroxide readily decomposes by itself. This report introduces a measurement example as below.
1) Determination of sulfuric acid by neutralization titration with sodium hydroxide・・・(1)
2) Determination of hydrogen peroxide by redox titration with potassium permanganate standard solution.・・・ (2) H₂SO₄ ＋ 2NaOH → Na₂SO₄ ＋ H₂O・・・(1) 5H₂O₂ ＋ 2KMnO₄ ＋ 3H₂SO₄ → K₂SO₄ ＋ 2MnSO₄ ＋ 8H₂O ＋ 5O₂・・・(2)
The control and analysis of nickel plating solution is very important process for the product quality. Analytical components of the general nickel plating solution are 1) nickel sulfamate, 2) nickel chloride, and 3) boric acid. The example of quantitative determination for total nickel which is total amount of nickel chloride and nickel sulfamate in nickel plating solution is introduced in this report. The total nickel is determined by photometric titration with EDTA standard solution using indicator MX. Ni(II) ＋ EDTA → Ni-EDTA
Copper sulfate plating is widely used in plating industries such as ornament, basic plating of anticorrosion plating, and plating for printed circuit board etc. This report introduces an example for determination of copper in copper sulfate plating solution with redox titration as follows: add potassium iodide to acidic sample to oxidize iodide by copper ion and generate free iodine (reaction 1). Titrate this free iodine with sodium thiosulfate to determine copper concentration (reaction 2) by redox titration. 2Cu²+ + 4I- → 2CuI + I₂・・・(1) I₂ + 2Na₂S₂O₃ → 2NaI + Na₂S₄O₆・・・(2)
Strong alkaline solution is used as remover for residual photoresist on the substrate after the development of the substrate for liquid crystal display instrument etc. The composition depends on the intended use but sodium hydroxide, potassium hydroxide, and tetramethylammonium hydroxide (TMAH) are used as remover.
TMAH can be determined by potentiometric titration with hydrochloric acid standard solution. TMAH could absorb carbon dioxide gas and generate carbonates, it indicates another inflection point at pH around 4 on the titration with hydrochloric acid standard solution. This report introduces an example of fractional determination for TMAH and carbonates. N(CH₃)₄OH ＋ HCl → N(CH₃)₄Cl ＋ H₂O・・・(1) [N(CH₃)₄]₂CO₃ ＋ HCl → N(CH₃)₄HCO₃ + N(CH₃)₄Cl・・・(2)
The reactions between TMAH and hydrochloric acid is described in formula (1), carbonate and hydrochloric acid is shown in formula (2). Carbonate generates hydrogen carbonate on reaction (2), it is continuously titrated with hydrochloric acid to the endpoint at around pH 4. The reaction between hydrogen carbonate salt and hydrochloric acid is indicated in formula (3). N(CH₃)₄HCO₃ ＋ HCl → N(CH₃)₄Cl ＋ CO₂ ＋ H₂O・・・(3)
Strong alkaline solution is used as remover for residual photoresist on the substrate after the development of the substrate for liquid crystal display instrument etc. The composition depends on the intended use but sodium hydroxide, potassium hydroxide, and tetramethylammonium hydroxide (TMAH) are used as remover.
TMAH can be determined by potentiometric titration with hydrochloric acid standard solution. TMAH could absorb carbon dioxide gas and generate carbonates, it indicates another inflection point at pH around 4 on the titration with hydrochloric acid standard solution. This report introduces an example of fractional determination for TMAH and carbonates. Barium chloride is added to determine carbonates; the precipitate of barium carbonate is generated on this method (formula (1)). [N(CH₃)₄]₂CO₃ ＋ BaCl₂ → [N(CH₃)₄Cl]₂ ＋ BaCO₃↓・・・(1)
This solution is titrated with hydrochloric acid. Only TMAH is determined at the first inflection point, and barium carbonate is determined at the second inflection point on the titration. N(CH₃)₄OH ＋ HCl → N(CH₃)₄Cl ＋ H₂O・・・(2) BaCO₃ ＋ 2HCl → BaCl₂ ＋ CO₂ ＋ H₂O・・・(3)
The reactions between TMAH and hydrochloric acid is described in formula (2), barium carbonate and hydrochloric acid is shown in formula (3). It reaches the endpoint at pH around 9 and 4 on the reaction (2) and (3), respectively. The titrant volume to determine carbonates gets twice on this method compared with the method without the addition of barium chloride. This method is useful especially for a sample containing less amount of carbonate.
Zinc ion can be readily determined by chelatometric titration. The titration with EDTA can be performed at the wide pH region (pH 4.5 ~ 10). The stability constant of Zn-EDTA complex is relatively large,1 there are a lot of highly sensitive indicator reagents for this titration. The report introduces an example that the sample adjusted to pH around 5.3 is photometrically titrated with EDTA titrant using XO indicator (red purple →yellow). Zn²⁺ ＋ Na₂EDTA → Zn-EDTA ＋ 2Na⁺
This report introduces an example of the determination of trace chloride ion in the solution containing highly concentrated copper sulfate.
The precipitation titration with silver nitrate standard solution is generally used for the determination of chloride ion in copper sulfate solution. The endpoint of the titration is detected with indicator method or the potentiometric method. The potentiometric method is used for this sample because the color change of indicator reagent is obscure in this sample containing highly concentrated copper sulfate. However, it tends to show the difficulty to detect the endpoint because of the less sensitivity of electrode under highly concentrated copper sulfate. Therefore the potentiometric titration is performed with the specially treated silver electrode that the silver chloride is coated. Cl- ＋ AgNO₃ → AgCl ＋ NO₃-
A wide variety of the determination methods for each component in acidic solution containing ferrous ion (Fe2+) and ferric ion (Fe3+) has been developed. This report introduces an example of the successive determination for ferric and ferrous ions in the steel cleaning solution.
First, Fe3+ ions are determined by chelatometric titration with EDTA at acidic pH using salicylic acid as the indicator (purple →yellow). The all Fe2+ ions are continuously oxidized to Fe3+ ion with ammonium peroxodisulfate. Finally, the Fe3+ ion oxidized from Fe2+ is determined by chelatometric titration with EDTA titrant as well as the above description. Fe³+ + Na₂EDTA → FeEDTA + 2Na+ Fe²+ → Fe³+ + e-
Manganese ion can be determined by chelatometric titration. The stability constant of Mn (II)-EDTA complex is relatively large (13.81),¹ but the suitable pH range for the reaction between manganese ion and EDTA is confined from 7 to 11. Since manganese ion is oxidized with air in alkaline solution, ascorbic acid or hydroxylamine is added for the titration to avoid the oxidation. The report introduces an example of the titration performed at alkaline condition (pH 10) adjusted by ammonia. Mn²+ + Na₂EDTA → Mn-EDTA + 2Na+
The chelatometric titration is generally used for the determination of lead ion (Pb2+). The pH region the lead ion can be directly titrated is pH 3.5 ~ 10 (stability constant = 17.88).1 However, it generates Pb(OH)2 precipitation at alkaline region. When performing titration under alkaline condition, the auxiliary complexing agent such as ethanolamine, tartaric acid, or citric acid should be added in advance to generate weak chelatometric complex and avoid the generation of lead hydroxide precipitation.
It is titrated at pH around 4 ~ 5 when performing under acidic condition. This report introduces an example that the lead ion in sample solution adjusted to pH 5 by hexamine solution is determined with using XO indicator (red purple →yellow). Pb²+ + Na₂EDTA → Pb-EDTA + 2Na+
The photometric titration using a photometric probe is generally applied for the determination of copper ion (Cu2+). However, the measurement of cloudy or colored sample has difficulty to analyze with the photometric titration. The measurement using copper ion-selective electrode performs the potentiometric titration which it is not affected by the suspended particle and the indicator reagent is not required for the titration. Cu²⁺ ＋ Na₂EDTA → Cu-EDTA ＋ 2Na²⁺ This report introduces an example of the measurement for copper ion in plating solution with chelatometric titration using copper ion-selective electrode.
Sodium hydroxide is one of the most elemental reagent in chemical industrial reagents. Its production amount is large and it is used in a broad range of fields. Sodium hydroxide absorbs carbonate gas and water in atmosphere because of its properties, the purity of sodium hydroxide is gradually reduced. Japanese Industrial Standard (JIS) K8576 defines determination method for purity of sodium hydroxide (titration with indicator). Representative impure substance in sodium hydroxide includes sodium carbonate.
This report introduces an example for the quantitative determination of sodium hydroxide purity and sodium carbonate by successive and fractional potentiometric titration.
First, sodium carbonate is precipitated as barium carbonate by adding barium chloride before the titration (formula (1)). Secondly, most sodium hydroxide is titrated with highly concentrated hydrochloric acid standard solution. After that, residual sodium hydroxide is titrated with low-concentrated hydrochloric acid standard solution. It enhances the accuracy of quantitative determination for sodium hydroxide. Barium carbonate generated on pretreatment is continuously titrated with low-concentrated hydrochloric acid standard solution. The titrated volume for carbonate is doubled compared with the procedure without adding barium chloride, so it is especially available for the small amount determination of carbonate. Na₂CO₃ + BaCl₂ → BaCO₃↓ ＋ 2NaCl (Pretreatment)・・・(1) NaOH ＋ HCl → NaCl ＋ H₂O・・・(2) BaCO₃ ＋ 2 HCl → BaCl₂ ＋ CO₂ ＋ H₂O (Titration)・・・(3)
The reaction between sodium hydroxide and hydrochloric acid is described in formula (2). Formula (3) shows the reaction between barium carbonate and hydrochloric acid. The pHs reach 9 and 4 on the reaction (2) and (3) at each end point.
Sodium hydroxide and sodium carbonate have important roles as alkali component chemicals, which are used in a broad range of industries. The concentration of both components have to be determined because these are sometimes used with mixed.
This report introduces an example that the mixture solution of sodium hydroxide and sodium carbonate are fractionally determined with potentiometric titration. The titration of sodium hydroxide and sodium carbonate with hydrochloric acid proceeds as the following reaction formula: NaOH + HCl → NaCl + H₂O・・・(1) Na₂CO₃ + HCl → NaHCO₃ + NaCl・・・(2)
The pH reaches around 9 at the end point on the reaction formula (1) and (2). Sodium carbonate generates sodium hydrogen carbonate (NaHCO3) on the reaction (2), then continuously generated sodium hydrogen carbonate is titrated with hydrochloric acid. It reaches the end point at pH around 4. The reaction between sodium hydrogen carbonate and hydrochloric acid is described in the formula (3). NaHCO₃ + HCl → NaCl + CO₂ + H₂O・・・(3)
The relation of titration curve and formula (1)(2)(3) is illustrated in the following figure.
Sodium hypochlorite is used for bleaching and sterilization of tap water because of its strong oxidizing and disinfecting properties. Sodium hypochlorite is relatively stable at the alkaline region. However, it is unstable at the acidic region and becomes hypochlorous acid (HClO). It oxidizes water and generates chlorine (Cl2). The concentration of available chlorine has to be measured regularly because sodium hypochlorite degrades slowly and generates sodium chloride.
This report introduces an example for determination of available chlorine as follows:.
1) Add potassium iodide to sodium hypochlorite to generate free iodine.
2) Titrate the free iodine generated from the reaction (1) with sodium thiosulfate to determine available chlorine (2) by redox titration. Cl₂ ＋2KI → I₂ ＋ 2KCl・・・(1) I₂ ＋ 2Na₂S₂O₃ → 2NaI ＋ Na₂S₄O₆・・・(2)
Sodium hypochlorite is produced by having sodium hydroxide absorb chlorine gas. Produced sodium hypochlorite contains sodium chloride generated by the degradation of hypochlorous acid.
This report introduces an example for the determination of residual alkali (sodium hydroxide, sodium carbonate) in the sodium hypochlorite with potentiometric titration. The procedure is described as follows: Add hydrogen peroxide to sodium hypochlorite to decompose the sodium hypochlorite (reaction (1)). Run neutralization titration with hydrochloric acid standard solution (reaction (2) ~ (4)). The pH reaches at around 8 on the reaction of (2) and (3). In the case of sodium carbonate, the sodium hydrogen carbonate generated on reaction (3) is continuously titrated with hydrochloride acid, and pH reaches to around 4 at the end point on the reaction (4). The reaction from (2) to (4) and related titration curve are illustrated in figure 1.
Titration volume for sodium hydroxide can be calculated by subtracting titration volume (b mL) of 2nd end point titration from titration volume (a+b mL) of 1st end point.
The concentration of sodium carbonate can be determined by titration volume of 2nd end point. Therefore sodium hydroxide and sodium carbonate can be determined separately with successive titration. Inflection point at around pH 11.5 is expected as the end point for sodium hydroxide, but the inflection point is unclear. Therefore it is not identified as the end point on this titration. NaClO + H₂O₂ → NaCl + H₂O + O₂・・・(1) NaOH + HCl → NaCl + H₂O・・・(2) Na₂CO₃ + HCl → NaHCO₃ + NaCl・・・(3) NaHCO₃ + HCl → NaCl + CO₂ + H₂O・・・(4)
Sodium hypochlorite is produced by having sodium hydroxide absorb chlorine gas. Produced sodium hypochlorite contains residual alkali (sodium hydroxide, sodium carbonate) and sodium chloride generated by the degradation of hypochlorous acid. The residual alkali is determined by neutralization titration, and sodium chloride is determined by precipitation titration. This report introduces an example of the determination for sodium chloride in the sodium hypochlorite with potentiometric titration as the following procedure: the titration for the total chlorine component (sodium hypochlorite + sodium chloride) is performed first. After that, sodium hypochlorite (available chlorine) is titrated by another method. Finally, sodium chloride is determined by the subtraction of sodium hypochlorite from the total chloride component.
The total sodium chloride (total chloride component) is determined according to the following formula (1) and (2): add hydrogen peroxide into a sample to degrade sodium hypochlorite, and generate sodium chloride as described in formula (1). Titrate with nitric acid standard solution until the pH goes down to 2 ~ 3. After the solution is acidified, determine the total sodium chloride with silver nitrate standard solution by precipitation titration as formula (2). NaClO + H₂O₂ → NaCl + H₂O + O₂・・・(1) NaCl + AgNO₃ → AgCl + NaNO₃・・・(2)
Regarding the determination of available chlorine, free iodine generated by the addition of potassium iodide as described in formula (3) is determined with sodium thiosulfate standard solution by redox titration as shown in formula (4). NaClO + 2KI ± H₂O → I₂ + NaCl + 2KOH・・・(3) I₂ + 2Na₂S₂O₃ → 2NaI + Na₂S₄O₆・・・(4)
Sulfuric acid is one of the most elemental reagent in chemical industrial reagents. Its production amount is large and it is used in a broad range of fields. Since sulfuric acid absorbs moisture in atmosphere because of its properties, the purity of sulfuric acid is gradually reduced. “JIS (Japanese Industrial Standards) K8951: 2006 Sulfuric acid (Reagent)” describes the determination method for purity of sulfuric acid which it is titrated with sodium hydroxide standard solution until the color of bromothymol blue indicator changes from yellow to blue green at the endpoint. However, this report introduces an example of the potentiometric titration with sodium hydroxide for the measurement of the accurately-weighed sample.
The neutralization titration for sulfuric acid with sodium hydroxide proceeds as two step reaction because sulfuric acid is diacid. However, the first and second dissociation of sulfuric acid cannot be discriminated due to the leveling effect of water. Therefore the single inflection point is observed on the titration curve and the reaction formula on this measurement can be described as below. H₂SO₄ + 2NaOH → Na₂SO₄ + H₂O・・・(1)
Phosphoric acid is important reagent as a raw material of chemical industrial reagents and fertilizers. Its production amount is large and it is used in a broad range of fields. The determination method of phosphoric acid purity is described in “JIS (Japanese Industrial Standards) K9005:2006 Phosphoric acid (reagent)”; the purity of phosphoric acid is determined by potentiometric titration with sodium hydroxide standard solution. This report introduces an example of the purity determination of phosphoric acid by this method.
Phosphoric acid reacts with sodium hydroxide as described in the reaction formula (1) ~ (3) because phosphoric acid is triacid. The titration curve of neutralization titration for phosphoric acid theoretically has three inflection points, but practically it shows two inflection points. This is because third acid dissociation constant (pKa) of phosphoric acid is 12.35, the pH at the third inflection point is undetectable value by the titration with strongly basic titrant. The purity of phosphoric acid is determined by the titration to the second inflection point in this measurement.
H₃PO₄ + NaOH → NaH₂PO₄ + H₂O・・・(1) NaH₂PO₄ + NaOH → Na₂HPO₄ + H₂O・・・(2) Na₂HPO₄ + NaOH → Na₃HPO₄ + H₂O・・(3)
The mixed solution of hydrochloric acid and sulfuric acid works as strong acid, and also has the strong oxidizability and solvency. It is used as the surface treatment solution for metals, glass products, and semiconductors. Hydrochloric acid and sulfuric acid are strong acids, therefore the fractional determination by neutralization titration is difficult.
The total acids of hydrochloric acid and sulfuric acid in the mixed solution are determined first by neutralization titration in this report. Nitric acid is added to the sample solution continuously to adjust the pH. Finally, the concentration of hydrochloric acid is determined by precipitation titration, the concentration of sulfuric acid is calculated by subtracting the concentration of hydrochloric from the total acids concentration.
The example of fractional determination for hydrochloric acid and sulfuric acid with additional burets are introduced in this report.
The mixed solution of nitric acid (inorganic acid) and acetic acid (organic acid) works as strong acid, and also has the strong oxidizability and solvency. It is used as the surface treatment solution for metals, glass products, and semiconductors.
This report introduces an example of the fractional and successive determination for nitric acid and acetic acid by neutralization titration with sodium hydroxide standard solution. HNO₃ + NaOH → NaNO₃ + H₂O・・・(1) CH₃COOH + NaOH → CH₃COONa + H₂O・・・(2)
Boric acid in plating solution is determined by neutralization titration. Boric acid cannot be directly determined by neutralization titration because it is too weak acid.
This report introduces an example of the procedure that D(-)-mannitol (mannite) is added to sample solution to generate stoicheiometric organic acid, and then it is titrated with sodium hydroxide standard solution. H₃BO₃ + C₆H₁₄O₆ → (C₆H₁₂O₆BO)H + 2H₂O・・・(1) (C₆H₁₂O₆BO)H + NaOH → (C₆H₁₂O₆BO)Na + H₂O・・・(2)
The mixed solution of nitric acid and phosphoric acid works as strong acid, and also has the strong oxidizability and solvency. It is used as the surface treatment solution for metals, glass products, and semiconductors.
This report introduces an example of the fractional and successive determination for nitric acid and phosphoric acid by neutralization titration with sodium hydroxide standard solution. When nitric acid and phosphoric acid are titrated by neutralization titration using a glass electrode for pH measurement, two inflection points appear on the titration curve. The first inflection point appears as the total amount of nitric acid and phosphoric acid (reaction formula (1) and (2)). Sodium dihydrogen phosphate, which is the product of reaction equation (2), subsequently reacts with sodium hydroxide and shows an inflection point in the second stage (reaction equation (3)). Therefore, it is possible to obtain the phosphoric acid concentration from the second inflection point, and nitric acid concentration could be obtained with subtracting titration volume at the second inflection point from the first inflection point.
Formic acid is monobasic carbonic acid , which belongs to lower saturated fatty acid group. Formic acid has a little different properties from other saturated fatty acids; it has significantly strong acidity (12 times stronger than acetic acid) and reducing character, degrades to water and carbon dioxide gas by the oxidation. It can also reduce ammoniacal silver nitrate.
The neutralization titration method with sodium hydroxide standard solution for the determination of
formic acid is prescribed in “JIS K8264. This report introduces an example of the potentiometric titration with glass electrode instead of indicator method using phenolphthalein prescribed in JIS.
Citric acid is oxycarboxylic acid which has carboxy group (-COOH) and alcoholic hydroxyl group (-OH).
It can be dissolved in water and has acidic property. Citric acid is produced as raw material of organic
compound or food additive.
“JIS K8283” prescribes the determination method for the purity of citric acid by the neutralization
titration using phenolphthalein indicator. This report introduces an example of the potentiometric titration (formula (1)) with sodium hydroxide standard solution for the purity determination of citric acid monohydrate according to “JIS K8283”.
Lactic acid is oxycarboxylic acid which has carboxy group (-COOH) and alcoholic hydroxyl group (-OH). It shows acidic property when dissolved in water. Lactic acid is produced as raw material of organic compound or food additive.
“JIS (Japanese Industrial Standards) K8726” prescribes the determination method for the lactic acid by the back-titration with sodium hydroxide and sulfuric acid using phenolphthalein indicator. This report introduces an example of the potentiometric titration (formula (1)) with sodium hydroxide standard solution for the measurement of lactic acid sanitizer solution for raw noodles.
Oxalic acid has two carboxy groups (-COOH) in the molecule , it is called dicarboxylic acid. There are two crystallization water molecules in the molecule. Oxalic acid is ortho acid and forms the following structure. It is readily oxidized by the acid stronger than formic acid.
Oxalic acid is used as raw material of organic compound. In addition, sodium salt of oxalic acid is used as standard substance of quantitative analysis because it quantitatively reacts with oxidizing agent like potassium permanganate and is stably conservable. The determination method for oxalic acid is prescribed in JIS K8519, it is determined by potassium permanganate standard solution. This report introduces an example of the purity determination for oxalic acid using redox titration as described below (formula 1) and neutralization titration with sodium hydroxide titrant (formula 2).
The mixed solution of acetic acid and ammonium acetate is used as washing solution on the production process of semiconductor. There are some determination methods for the fractional determination of a weak acid and a salt of a weak acid. The formaldehyde addition method which is the most typical determination method is introduced in this report.
First, the neutralization titration is performed for acetic acid with sodium hydroxide (formula (1)). After that, acetic acid and hexamethylenetetramine equivalent to ammonium acetate are generated by adding formaldehyde (formula (2)). Finally, the generated acetic acid is continuously titrated with sodium hydroxide to determine the ammonium acetate.
Ascorbic acid has properties as an acid and a strong reducing agent. On the other hand, sodium ascorbate doesn’t have a function as an acid but works as a reducing agent as well as ascorbic acid. The quantitative determination method for ascorbic acid is prescribed in JIS K 9502 and Japanese pharmacopeia. There are two determination methods for ascorbic acid; neutralization titration and iodine titration.
The fractional determination method for ascorbic acid and sodium ascorbate is introduced in this report. First, ascorbic acid is determined by the neutralization titration with sodium hydroxide standard solution (formula (1)). After that, the total amount of ascorbic acid (ascorbic acid and sodium ascorbate) is measured by the redox titration with iodine standard solution (formula (2) and (3)). The sodium ascorbate is determined by the subtraction of the ascorbic acid from the total amount of ascorbic acid.
Peracetic acid (CH₃COOOH) is used as oxidizing agent, bleaching agent, and fungicide. Peracetic acid generates acetic acid and oxygen by its decomposition. It is suggested that the bleaching and antiseptic properties are derived from this generated oxygen. On the other hand, hydrogen peroxide (H₂O₂) works as both oxidizing and reducing agents depending on the target chemical to be reacted. It is used as fungicide in food industry as well as peracetic acid.
Recently, the usage of the mixed solution containing hydrogen peroxide, peracetic acid, and acetic acid has been increasing for the sterilization of beverage containers along with the popularization of a plastic bottle as containers. This report introduces an example of fractional determination of hydrogen peroxide and peracetic acid in the mixed solution containing hydrogen peroxide, peracetic acid, and acetic acid.
The fractional titration of hydrogen peroxide and peracetic is performed as follows: first, hydrogen peroxide is titrated with potassium permanganate standard solution (formula (1)) after the sample solution is acidified with sulfuric acid. After the titration, add potassium iodide to generate iodine equivalent to peracetic acid (formula (2)). This generated iodine is titrated with sodium thiosulfate standard solution to determine the peracetic acid (formula (3)).
The acid number of lubricant oil is one of the important index for judging its quality.
Measurement of acid number is defined in several standard test methods. It is indicated by “milligrams of potassium hydroxide required to neutralize acidic components contained in 1 g of the sample”.
The international standard methods for acid number are shown as bellow.
・ JIS K2501 2003：Petroleum products and lubricants – Determination of neutralization number
・ ASTM D664-1995 : Standard Test Method for Acid Number of Petroleum Products by Potentiometric Titration
The potentiometric titration process is as follows:
1) Weigh sample exactly corresponding to acid number and dissolve it in a titration solvent.
2) Immerse glass electrode and reference electrode.
3) Start titration with alcoholic potassium hydroxide solution.
Inflection point is defined as the end point if it obtained sharply. If it’s not clear, the pH obtained from measurement of buffer solution is defined as the end point. The measurement with the latter end point detection will be introduced here.
The base number of lubricant oil is one of the important index for judging its quality. Measurement of base number is defined in several standard test methods. It is indicated by “milligrams of potassium hydroxide equivalent weight to acid required to neutralize basic components contained in 1 g of the sample”. There are two methods of base number, hydrochloric acid method and perchloric acid method. In this article, hydrochloric acid method will be introduced. The international standard methods for base number with hydrochloric acid method are shown as bellow.
・ JIS K2501 2003 : Petroleum products and lubricants – Determination of neutralization number
・ ASTM D4739-2011 : Standard Test Method for Base Number Determination by Potentiometric Hydrochloric Acid Titration
The potentiometric titration process is as follows:
1) Weigh sample exactly corresponding to base number and dissolve it in a titration solvent.
2) Immerse glass electrode and reference electrode.
3) Start titration with alcoholic hydrochloric acid solution.
Inflection point is defined as the end point if it obtained sharply. If it’s not clear, the pH obtained from measurement of buffer solution is defined as the end point. The measurement with the latter end point detection will be introduced here.
The base number of lubricant oil is one of the important index for judging its quality. Measurement of base number is defined in several standard test methods. It is indicated by “milligrams of potassium hydroxide equivalent weight to acid required to neutralize basic components contained in 1 g of the sample”. There are two methods of base number, hydrochloric acid method and perchloric acid method. In this article, perchloric acid method will be introduced. The international standard methods for base number with perchloric acid method are shown as bellow.
・ JIS K2501 2003 : Petroleum products and lubricants – Determination of neutralization number
・ ASTM D2896-06 : Standard Test Method for Base Number of Petroleum Products by Potentiometric Perchloric Acid Titration
The potentiometric titration process is as follows:
1) Weigh sample exactly corresponding to base number and dissolve it in a titration solvent.
2) Immerse glass electrode and reference electrode.
3) Start titration with perchloric acid in acetic acid solution.
There are two procedures for perchloric acid titration, A and B on ASTM D2896. Procedure A and B use different titration solvent volume and sample weight. In this article, measurement with procedure B will be applied. Inflection point is defined as the end point if it obtained sharply. If it’s not clear, back-titration method could be applied. Back-titration method is mentioned in “HIRANUMA APPLICATION DATA No. L11”.
Refrigerating machine oil is used in a state mixed with refrigerant such as hydrofluorocarbon. The official standard of refrigerant (e.g. JIS K 2211) specifies the acid number test according to JIS K 2501. It is indicated by “milligrams of potassium hydroxide required to neutralize acidic components contained in 1 g of the sample”.
In this article, we apply the color-indicator titration method described in JIS K2501 to automatic titrator, and introduce measurement of acid number in refrigerating machine oil by photometric titration. Acid and base number with color-indicator titration is also regulated in ASTM D974. p-Naphtholbenzein is used as color indicator.
The base number of lubricant oil is one of the important index for judging its quality.
Measurement of base number is defined in several standard test methods. It is indicated by “milligrams of potassium hydroxide equivalent weight to acid required to neutralize basic components contained in 1 g of the sample”. There are two methods of base number, hydrochloric acid method and perchloric acid method. In addition, there are two types of perchloric acid titration, forward-titration and back-titration. In this article, perchloric acid method with back-titration will be introduced. The international standard methods for base number with perchloric acid method are shown as bellow.
・ JIS K2501 2003：Petroleum products and lubricants – Determination of neutralization number
・ ASTM D2896-06 : Standard Test Method for Base Number of Petroleum Products by Potentiometric Perchloric Acid Titration
The potentiometric titration process is as follows:
1) Weigh sample exactly corresponding to base number and dissolve it in a titration solvent.
2) Immerse glass electrode and reference electrode.
3) Add fixed amount of perchloric acid in acetic acid solution to the sample.
4) Start titration with sodium acetate in acetic acid solution.
There are two procedures for perchloric acid titration with back-titration, A and B on ASTM D2896. Procedure A and B use different titration solvent volume and sample weight. In this article, measurement with procedure B will be applied.
Epoxy resins have competent characteristics such as chemical resistance, heat resistance, and electrical properties. They are widely used for various materials like sealant of electronic device (IC).
Epoxy resin is generic name of compounds which have two or more epoxy group in one molecule, it does not harden by itself. The addition of catalyst or hardener is required for curing. It becomes thermoset resin through addition polymerization with epoxy group by the hardener (fatty amine etc.). The additive amount of hardener corresponds to epoxy equivalent (mass of resin including one-equivalent epoxy group) of each epoxy resin. The determination of epoxy equivalent is quite important process for quality control. The measurement method of epoxy equivalent is defined in JIS (Japanese Industrial Standards) K7236:2001. Measurement is performed as follows:
1) Weigh the sample accurately and dissolve it in chloroform.
2) Add acetic acid and tetraethyl ammonium bromide – acetic acid solution.
3) Perform potentiometric titration with 0.1 mol/L perchloric acid – acetic acid standard solution.
Perchloric acid reacts with tetraethylammonium bromide and generates hydrogen bromide by addition of perchloric acid – acetic acid standard solution. (Refer to the reaction formula 1-1.)
The generated hydrogen bromide reacts with epoxy group. (Refer to the reaction formula 1-2.)
When all epoxy groups are reacted and hydrogen bromide gets excess, this point is detected as the endpoint to determine epoxy equivalent.
(C₂H₅)₄NBr + HClO₄ → HBr + (C₂H₅)₄NClO₄・・・(1-1) ・・・(1-2)
ASTM E1899 : Standard Test Method for Hydroxyl Groups Using Reaction with p-Toluenesulfonyl Isocyanate (TSI) and Potentiometric Titration with Tetrabutylammonium Hydroxide
Synthetic adhesives like hydrophilic macromolecule –Isocyanate type wood adhesives are consisted of base compound and cross-linker; the principal components of base compound are macromolecule aqueous solution or aqueous dispersing element, or those combination. The principal components of cross-linker is isocyanate compounds. The measurement procedure of isocyanate (NCO) content described in this report is standardized by JIS K 6806. NCO content is determined by the neutralization titration which excess di-n-butylamine is titrated with hydrochloric acid standard solution after sample and di-n-butylamine are mixed and reacted. A measurement example of potentiometric titration for NCO determination is introduced in this report.
ASTM D5155 : Standard Test Methods for Polyurethane Raw Materials: Determination of the Isocyanate Content of Aromatic Isocyanates
This report introduces an example of the determination of chloride ion in cement.
This measurement method is described in “Method for measuring chloride” of “Japanese industrial standard JIS R 5202 Method for chemical analysis of cements”. The sample is dissolved in nitric acid, a chloride ion standard solution and a hydrogen peroxide solution are added, and the sample is heat-treated, and then the measurement is performed by precipitation titration using a silver nitrate standard solution. The measurements are made by potentiometric titration using a chloride ion-selective electrode as the electrode for end point detection.
This report introduces an example of the determination of chloride ion in concrete.
This measurement method is described in “Potentiometric titration method using chloride ion-selective electrode” of “JIS A 1154 Method of test for chloride ion content in hardened concrete”. Nitric acid is added to adjust the pH to 3 or less, and extract chloride ion with boiling. Cool to room temperature, filtrate to separate undissolved component and collect filtrated solution as sample. Chloride ion is determined by precipitation titration using a silver nitrate standard solution.
The measurement method of alkaline substance by neutralization titration using a hydrochloric acid standard solution is widely used in the titration analysis. Factors are indicated on the commercially available standard solution for volumetric analysis. The factor determination is required when the standard solutions are prepared in the laboratory.
In this report, the above two types of standardization methods were performed. When amidosulfuric acid is used for the standard substance, firstly a known amount of amidosulfuric acid is dissolved in pure water. And then potentiometric titration is performed with 0.1 mol/L sodium hydroxide standard solution to determine its factor.
Sodium thiosulfate standard solution is used as a titrant for iodometric titration method. In iodometric titration, an equivalent amount of iodine (I2) is produced by reacting the oxidant component in measurement sample with the added potassium iodide (KI). The generated iodine (I2) is titrated with sodium thiosulfate standard solution, which enables the titration of the oxidant component indirectly.
In this report, sodium chloride, which is a standard material, was dissolved in pure water, and potentiometric titration was performed with 0.1 mol/L silver nitrate standard solution to determine the factor. 1 mol of sodium chloride and 1 mol of silver nitrate react quantitatively according to Eq. (1), and the titration curve shows an inflection point at the end point.
This report introduces the factor determination method for ammonium thiocyanate standard solution. Firstly, 0.1 mol/L silver nitrate standard solution, which is a standard material, was dispensed with a buret. Secondly, potentiometric titration was performed with ammonium thiocyanate standard solution to determine the factor of ammonium thiocyanate.
Non-aqueous titration using a 0.1 mol/L perchloric acid-acetic acid solution (hereinafter referred to as perchloric acid titration) has been used for test methods such as JIS K2501 “Petroleum products and lubricants – Determination of neutralization number” and determination of purity for some substance in the Japanese Pharmacopoeia. Weakly basic components that hardly react with a titrant in water can be quantified by neutralization titration with the perchloric acid titration.
Iodine (I2) is an oxidant and its redox pair is an iodide ion(I-). In the iodometric titration method, an excessive amount of iodide ion(I-) is reacted with the oxidizing agent in the sample. The produced iodine(I2) is titrated with sodium thiosulfate and the oxidant is indirectly quantified. This method is widely used to quantify oxidants. On the other hand, in the iodimetric titration method, the reducing agent in the sample is directly titrated with an iodine(I2) titrant: example of its use is the quantification of sulfites.
Potassium permanganate is a strong oxidizing agent, thus the potassium permanganate standard solution is used as a titrant for reducing agents such as iron(II) iron, and as a titrant for hydrogen peroxide and chemical oxygen demand (COD).
Ammonium iron (II) sulfate is a reducing agent and is used as a titrant in redox titration because it has relatively stable properties among iron (II) compounds. The following are examples of usage: first, an excessive amount of potassium permanganate is added to react with target metal compound, such as chromium or vanadium, contained in the sample. Next, the potassium permanganate that remains unreacted is titrated with an ammonium iron(II) sulfate standard solution to indirectly quantify the target metal compound.
Disodium dihydrogen ethylenediamine tetraacetate (hereinafter referred to as EDTA) is a chelating agent and has the property of forming chelate compounds with many metal ions. It is used as a titrant for a chelatometric titration method to quantify metal ions. The chelatometric titration method has a wide range of applications, various metal ions could be measured with the use of appropriate indicator reagent and pH.
Water content of hydrocarbon and halogenated hydrocarbon could be determined by Karl Fischer coulometric titrator. In coulometric titration, iodine of Karl Fischer reagent is generated by electrolysis and generated iodine quantitatively reacts with water. Reaction formula is described below.
Hydrocarbon and halogenated hydrocarbon do not interfere the Karl Fischer reaction and direct injection method could apply. Anode solution is selected in accordance with sample solubility. General use of anode solution contain methanol as solvent. When the sample like a long chain hydrocarbon have poor solubility in methanol, anode solution containing chloroform or hexanol or toluene is used. When fritless cell is used, cathode solution is not necessary.
Water content of Alcohols is determined by Karl Fischer coulometric titrator. In coulometric titration, iodine of Karl Fischer reagent is generated by electrolysis and generated iodine quantitatively reacts with water. Reaction formula is described below.
Alcohols do not interfere the Karl Fischer reaction and direct injection method could apply. Anode solution is selected in accordance with sample solubility. General-use anode solution contains methanol as solvent. Alcohols with long carbon chain have low solubility in methanol. In that case, use of anode solution for oil is appropriate.
When fritless cell is used, cathode solution is not necessary.
Water content of Aromatic hydrocarbons are determined by Karl Fischer coulometric titrator. In coulometric titration, iodine of Karl Fischer reagent is generated by electrolysis and generated iodine quantitatively reacts with water. Reaction formula is described below.
Aromatic hydrocarbons do not interfere the Karl Fischer reaction and direct injection method could apply. Anode solution is selected from General-use or Oil in accordance with sample solubility. General-use anode solution contains methanol as solvent. When the sample has low solubility in methanol, the use of anode solution for oil is appropriate. When fritless cell is used, cathode solution is not necessary.
Water content of Oil products are determined by Karl Fischer coulometric titrator. In coulometric titration, iodine of Karl Fischer reagent is generated by electrolysis and generated iodine quantitatively reacts with water. Reaction formula is described below.
Kerosene and diesel oil do not interfere the Karl Fischer reaction and direct injection method could apply. Anode solution for Oil is selected to dissolve samples.
It is known that some of the oil additives interfere Karl Fischer reaction. In that case, azeotropic distillation method with Oil evaporator is appropriate. Water is separated from oil sample by distillation and introduced to electrolytic cell with carrier gas.
Mercaptanes and hydrogen sulfide in oil interfere Karl Fischer reaction. Since these side reactions occur quantitatively, water content result could be corrected with concentration of mercaptanes and hydrogen sulfide. 1 ppm of mercaptanes or hydrogen sulfide lead 0.3 ppm or 0.6 ppm higher water content respectively.
ASTM D6304 : Standard Test Method for Determination of Water in Petroleum Products, Lubricating Oils, and Additives by Coulometric Karl Fischer Titration
ASTM E1064 : Standard Test Method for Water in Organic Liquids by Coulometric Karl Fischer Titration
ASTM D4928 : Standard Test Method for Water in Crude Oils by Coulometric Karl Fischer Titration
Water content of Ethers and Esters are determined by Karl Fischer coulometric titrator. In coulometric titration, iodine of Karl Fischer reagent is generated by electrolysis and generated iodine quantitatively reacts with water. Reaction formula is described below.
Ethers and esters do not interfere the Karl Fischer reaction and direct injection method could apply. Anode solution is selected from General-use or Oil in accordance with sample solubility. General-use anode solution contains methanol as solvent. When the sample has low solubility in methanol, the use of anode solution for oil is appropriate. One exception is a sample containing vinyl group, which reacts with KF reagent and interferes the titration. When fritless cell is used, cathode solution is not necessary.
Water content of amines could be determined by Karl Fischer coulometric titrator. In coulometric titration, iodine of Karl Fischer reagent is generated by electrolysis and generated iodine quantitatively reacts with water. Reaction formula is described below.
The amines change anode solution pH to basic. In the case of an amine with stronger basicity than benzylamine (pKa = 9.34¹)) as a guideline, there are such effects as the end point becomes unclear. Therefore, when measuring a strongly basic amine, add a neutralizing agent to the anode solution beforehand to suppress the influence of undesirable effect caused by adding the sample. This application introduces an example for the water determination in cyclohexylamine(liquid), diethanolamine(liquid) and imidazole(solid). Reference
1) H. K. Hall, J. Am. Chem. Soc. (1957) 79 5441.
Water content of Nitriles could be determined by Karl Fischer coulometric titrator. In coulometric titration, iodine of Karl Fischer reagent is generated by electrolysis and generated iodine quantitatively reacts with water. Reaction formula is described below.
Nitriles do not interfere the Karl Fischer reaction and direct injection method could apply. Anode solution is selected in accordance with sample solubility. General use of anode solution contain methanol as solvent. When the sample like a long chain hydrocarbon has poor solubility in methanol, anode solution containing chloroform or hexanol or toluene is used.
Water content of oil products are determined by Karl Fischer coulometric titrator. In coulometric titration, iodine of Karl Fischer reagent is generated by electrolysis and generated iodine quantitatively reacts with water. Reaction formula is described below.
Generally the fuel oil does not interfere the Karl Fischer reaction and direct injection method could apply. Suitable anode solution is selected for dissolving oil samples.
It is known that some of the oil additives interfere Karl Fischer reaction. In that case, azeotropic distillation method with Oil evaporator is appropriate. Water is separated from oil sample by distillation and introduced to electrolytic cell with carrier gas.
ASTM D6304 : Standard Test Method for Determination of Water in Petroleum Products, Lubricating Oils, and Additives by Coulometric Karl Fischer Titration
Water contents of drugs and medicines could be determined by Karl Fischer coulometric titrator. In coulometric titration, iodine of Karl Fischer reagent is generated by electrolysis and generated iodine quantitatively reacts with water. Reaction formula is described below.
When the moisture content is relatively high at the% level, the amount of sample added is as small as a few 10 mg. If the sample is in powder form, taking and adding samples with an “ultra-micro solid sampler” makes measurement easy and accurate. An example for water contents measurements of thiamine chloride hydrochloride and folic acid performed by with ultra-micro solid sampler are introduced here. The measurement method was determined with reference to Japanese Pharmacopeia. Reference
1) Japanese Pharmacopoeia Seventeenth Edition
Water contents of drugs and medicines could be determined by Karl Fischer volumetric titrator. In volumetric titration, titrant have a titer which means the capacity to react with water per 1 mL of titrant. Factor is pre-determined before sample measurement and water content of sample is calculated from consumed titrant volume within sample measurement.
When the sample is liquid, generally sample is measured by direct injection into the cell. Dehydrated methanol is used for titration solvent. The titration solvent may change to a composition suitable for dissolving the sample.
Examples for water contents measurements of propylene glycol and glycerin performed by direct injection method are introduced here. The measurement method was determined with reference to Japanese Pharmacopeia.
Reference
1) Japanese Pharmacopoeia Seventeenth Edition
ASTM E203 : Standard Test Method for Water Using Volumetric Karl Fischer Titration
ASTM D4377 : Standard Test Method for Water in Crude Oils by Potentiometric Karl Fischer Titration
ASTM D890 : Standard Test Method for Water in Liquid Pine Chemicals
Water contents of drugs and medicines could be determined by Karl Fischer volumetric titrator. In volumetric titration, the titrant have a factor which means the ability to react with how many milligrams of water per 1 mL of titrant. Factor is pre-determined before sample measurement and water content of sample is calculated from consumed titrant volume within sample measurement.
There are two methods in KF volumetric titration, forward-titration and back-titration. Forward-titration is used in general. However, some of the sample should be measured by back-titration method according to Pharmacopeias. In back-titration method, firstly excess amount of KF titrant is added to the water contained in the sample, and then the remaining unreacted of KF titrant is titrated with water-in-methanol solution. Therefore, it is necessary to measure the factor not only KF titrant but also the water-in-methanol before the sample measurement.
An example for water contents measurements of dextromethorphan hydrobromide monohydrate performed by back-titration method is introduced here. The measurement method was determined with the reference to Japanese Pharmacopeia. Please refer to Application Data No. 22 for the suitability test of Japanese Pharmacopoeia eighteenth edition by the back titration method.
Reference
1) Japanese Pharmacopoeia Eighteenth Edition
Water contents of drugs and medicines could be determined by Karl Fischer volumetric titrator. In volumetric titration, titrant have a titer which means the capacity to react with water per 1 mL of titrant. Factor is pre-determined before sample measurement and water content of sample is calculated from consumed titrant volume within sample measurement.
When the sample is solid, firstly sample is measured by direct injection into the cell. Dehydrated methanol is used for titration solvent. The titration solvent may change to a composition suitable for dissolving the sample. If the sample is insoluble to titration solvent, heat-evaporation method is appropriate to these samples. An example for water contents measurements of sodium lauryl sulfate and benzalkonium chloride performed by direct injection method are introduced here. The measurement method was determined with reference to Japanese Pharmacopeia.
Reference
1) Japanese Pharmacopoeia Seventeenth Edition
Water contents of drugs and medicines are usually determined by Karl Fischer volumetric titrator. In volumetric titration, titrant have a factor which means the capacity to react with water per 1 mL of titrant. Factor is pre-determined before sample measurement and water content of sample is calculated from consumed titrant volume within sample measurement.
This application introduces an example for the water determination in lactose hydrate and L-histidine hydrochloride hydrate with reference to Japanese Pharmacopeia. Sample is measured by direct injection into the cell. When the solubility of the sample in methanol is not sufficient, use a mixed solvent of methanol and formamide as the titration solvent.
Reference
1) Japanese Pharmacopoeia Seventeenth Edition
Water contents of ketones and aldehydes could be determined by Karl Fischer volumetric titrator. In volumetric titration, titrant have a factor which is the capacity to react with water per 1 mL of titrant. Factor is pre-determined before sample measurement and water content of sample is calculated from consumed titrant volume by sample measurement.
When the sample is liquid, generally sample is measured by direct injection into the titration cell. Dehydrated methanol is generally used for titration solvent. However, in the measurement of ketones and aldehydes, since these react with methanol to produce water, the measurement result tends to be higher than the true value (formula (1)). R₂CO + 2CH₃OH → R₂C(OCH₃)₂ + H₂O ・・・(1)
For above reason, Karl Fischer reagent without methanol should be used for water determination of ketones and aldehydes. There are commercially available reagents with a special composition for ketones and aldehydes. This chapter introduces an example for the water determination in methyl ethyl ketone, acetone and cyclohexanone with water added to them to 1 %. These samples are often used as paint solvents, raw materials of adhesives, and synthetic resins.
Water content of ketones could be determined by Karl Fischer coulometric titrator. In coulometric titration, iodine of Karl Fischer reagent is generated by electrolysis and generated iodine quantitatively reacts with water. Reaction formula is described below. H₂O ＋ I₂ ＋ SO₂ ＋ 3RN ＋ CH₃OH → 2RN・HI ＋ RN・HSO₄CH₃ 2RN・HI → I₂ ＋ 2RN ＋ 2H⁺ ＋ 2e⁻
When the sample is liquid, generally sample is measured by direct injection into the titration cell. Anode solution containing methanol as solvent is generally used for various sample. However, in the measurement of ketones and aldehydes, since these react with methanol to produce water, the measurement result tends to be higher than the true value (formula (1)). R₂CO + 2CH₃OH → R₂C(OCH₃)₂ + H₂O ・・・(1)
For above reason, Karl Fischer reagent without methanol should be used for water determination of ketones and aldehydes. There are commercially available reagents with a special composition for ketones and aldehydes. This chapter introduces an example for the water determination in methyl ethyl ketone and acetone. These samples are often used as paint solvents, raw materials of adhesives, and synthetic resins.
Water content of cyclohexanone is determined by Karl Fischer coulometric titrator. In coulometric titration, iodine of Karl Fischer reagent is generated by electrolysis and generated iodine quantitatively reacts with water. Reaction formula is described below.
H₂O ＋ I₂ ＋ SO₂ ＋ 3RN ＋ CH₃OH → 2RN・HI ＋ RN・HSO₄CH₃ 2RN・HI → I₂ ＋ 2RN ＋ 2H⁺ ＋ 2e⁻
Ketones and aldehydes would interfere the Karl Fischer reaction by side-reaction with methanol (formula (1)).
R₂CO + 2CH₃OH → R₂C(OCH₃)₂ + H₂O ・・・(1) Therefore it is necessary to use methanol-free anode and cathode solution. There are commercially available reagents with a special composition for ketones and aldehydes. However, cyclohexanone has particularly a strong side reaction activity, so it is difficult to measure by direct injection method at room temperature. In the measurement of cyclohexanone, it is effective to lower the activity of side reaction by cooling or to separate cyclohexanone and water by distillation.
This application introduces an example for the water determination in cyclohexanone with cooled direct injection method and azeotropic distillation method
Water contents of sugars could be determined by Karl Fischer volumetric titrator. In volumetric titration, titrant have a factor which means the capacity to react with water per 1 mL of titrant. Factor is pre-determined before sample measurement and water content of sample is calculated from consumed titrant volume by sample measurement.
This application introduces an example for the water determination in glucose, fructose, and sucrose. Sugars have tendency to dissolve in formamide. Therefore a mixed solvent of formamide and methanol was chosen as the titration solvent.
A heat evaporation method using Karl Fischer titrator combined with solid evaporator is suitable for insoluble sample in anode solution, such as plastics and inorganic compounds. The measurement of with the heat evaporation method is carried out by heating the sample while a carrier gas is blown into the evaporation chamber and introducing the evaporated moisture together with the carrier gas into the electrolysis cell.
This application introduces an example of measurement of solid water standard for validation of titrator system with solid evaporator.
Water contents of granulated sugar could be determined by Karl Fischer volumetric titrator. In volumetric titration, titrant have a factor which means the amount to react with water per 1 mL of titrant. The factor is pre-determined before sample measurement and water content of sample is calculated from the consumed titrant volume by sample measurement.
This application introduces an example for the water determination in granulated sugar. Due to the low water content of this sample, a relatively large amount of sample must be added, but the solubility in methanol as titration solvent is not sufficient. Sugars have tendency to dissolve in formamide. Therefore a mixed solvent of formamide and methanol was chosen as the titration solvent. To make it easier to dissolve the sample, the titration cell was heated to 45 °C using an outer chamber for flowing warm water.
Since the water content of the granulated sugar is often a few hundred ppm, the titrant with low factor value, as 1 mg/mL was used. When pure water is used as the standard material of factor standardization for low factor titrant, the amount of pure water added should be as small as 10 to 20 mg, which makes accurate addition and weighing difficult. Therefore, water standard material which is the solution containing 1 % of water sealed in glass ampoule is used for the factor standardization.
Water contents of drugs and medicines could be determined by Karl Fischer volumetric titrator. In volumetric titration, the titrant have a factor which means the ability to react with how many milligrams of water per 1 mL of titrant. Factor is pre-determined before sample measurement and water content of sample is calculated from consumed titrant volume within sample measurement.
In the method of “Water determination (Karl Fischer method)” in Japanese Pharmacopoeia Eighteenth Edition, the suitability test is described as a verification procedure when modifying the test procedures. In this report, a case example of suitability test is introduced with using glycerin as a simulated measurement sample.
Water contents of drugs and medicines could be determined by Karl Fischer coulometric titrator. In coulometric titration, iodine of Karl Fischer reagent is generated by electrolysis and generated iodine quantitatively reacts with water.
In the method of “Water determination (Karl Fischer method)” in Japanese Pharmacopoeia Eighteenth Edition, the suitability test is described as a verification procedure when modifying the test procedures. As premises for complying the suitability test, it is possible to select and use the appropriate KF reagent from commercially available products.
In this report, the suitability test of Japanese Pharmacopoeia Eighteenth Edition was performed for thiamine chloride hydrochloride, also introduced in Application Data No. 9, with coulometric titration method. Please refer to Application Data No. 9 for the detail of sample addition procedure and the repeatability of measurement results for thiamine chloride hydrochloride.
Water contents of drugs and medicines could be determined by Karl Fischer volumetric titrator. In volumetric titration, the titrant have a factor which means the ability to react with how many milligrams of water per 1 mL of titrant. Factor is pre-determined before sample measurement and water content of sample is calculated from consumed titrant volume within sample measurement.
There are two methods in KF volumetric titration, forward-titration and back-titration. Forward-titration is used in general. However, some of the sample should be measured by back-titration method according to Pharmacopeias.
In this report, the suitability test of Japanese Pharmacopoeia Eighteenth Edition was performed for dextromethorphan hydrobromide monohydrate, also introduced in Application Data No. 11, with back-titration method. Please refer to Application Data No. 11 for the factor determination of titrants procedure and the repeatability of measurement results for dextromethorphan hydrobromide monohydrate.
When using this homepage, we recommend Chrome browser. Chrome can translate web pages.
･･･(1)
･･･(1)
･･･(1)
・・・(1-2)