6. Apparatus
6.1 Buret - A 25 mL buret graduated in 0.1 mL subdivisions, or a 10 mL buret graduated in 0.05 mL subdivisions.
NOTE 1 - An automated buret capable of delivering titrant amounts in 0.05 mL or smaller increments can be used, but the stated precision data were obtained using manual burets only.
7. Reagents and Materials
7.1 Purity of Reagents - Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that all reagents shall conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society, where such specifications are available. Other grades may be used, provided it is first ascertained that the reagent is of sufficiently high purity to permit its use without lessening the accuracy of the determination.
NOTE 2 - Commercially available reagents may be used in place of laboratory preparations when they are certified in accordance with 7.1.
7.2 Purity of Water - References to water shall be understood to mean distilled water as defined by Type III water of Specification D1193.
7.3 p-Naphtholbenzein Indicator Solution - The p-naphtholbenzein must meet the specifications given in Annex A1. Prepare a solution of p-naphtholbenzein in titration solvent equal to 10 g/L +/- 0.01 g/L.
7.4 Nitrogen, dry-type, carbon dioxide-free. (Warning - Compressed gas under high pressure. Gas reduces oxygen available for breathing.)
7.5 Potassium Hydroxide Solution, Standard Alcoholic (0.01 N) - Add 0.6 g of solid KOH (Warning - Highly corrosive to all body tissue both in solid form and in solution.) to approximately 1 L of anhydrous isopropyl alcohol (Warning - Flammable. Vapor harmful. Keep away from heat, sparks, and open flame.) (containing less than 0.9 % water) in a 2 L Erlenmeyer flask. Boil the mixture gently for 10 min to 15 min, stirring to prevent the solids from forming a cake on the bottom. Add at least 0.2 g of barium hydroxide (Ba(OH)2) (Warning - Poisonous if ingested. Strongly alkaline, causes severe irritation producing dermatitis.) and again boil gently for 5 min to 10 min. Cool to room temperature, allow to stand for several hours, and filter the supernatant liquid through a fine sintered-glass or porcelain filtering funnel; avoid unnecessary exposure to carbon dioxide (CO2) during filtration. Store the solution in a chemically resistant dispensing bottle out of contact with cork, rubber, or saponifiable stopcock lubricant and protected by a guard tube containing soda lime.
NOTE 3 - Because of the relative large coefficient of cubic expansion of organic liquids, such as isopropyl alcohol, the standard alcoholic solutions should be standardized at temperatures close to those employed in the titration of samples.
7.5.1 Standardization of Potassium Hydroxide Solution - Standardize frequently enough to detect changes of 0.0002N. One way to accomplish this is as follows. Weigh, to the nearest 0.1 mg, approximately 0.02 g of potassium acid phthalate, which has been dried for at least 1 h at 110 °C +/- 1 °C and dissolve in 40 mL +/- 1 mL of water, free of CO2. Titrate with the potassium hydroxide alcoholic solution to either of the following end points: (1) when the titration is electrometric, titrate to a well-defined inflection point at the voltage that corresponds to the voltage of the basic buffer solution; (2) when the titration is colorimetric, add 6 drops of phenolphthalein indicator solution and titrate to the appearance of a permanent pink color. Perform the blank titration on the water used to dissolve the potassium acid phthalate. Calculate the normality using the equation:
where:
Wp = weight of the potassium acid phthalate, g,
204.23 = molecular weight of the potassium acid phthalate,
V = volume of titrant used to titrate the salt to the specific end point, mL, and
Vb = volume of titrant used to titrate the blank, mL.
7.5.2 Phenolphthalein Indicator Solution - Dissolve 0.1 g +/- 0.01 g of pure solid phenolphthalein in 50 mL of water, free of CO2, and 50 mL of ethanol.
7.6 Titration Solvent - Add 500 mL of toluene (Warning - Flammable. Vapor harmful. Keep away from heat, sparks, and open flame.) and 5 mL of water to 495 mL of anhydrous isopropyl alcohol.