6. Apparatus
6.1 Potentiometric Titrimeter, automatic or manual, with capability of adding fixed increments of titrant at fixed time intervals (see Annex A1).
6.1.1 The titrimeter must automatically (or manually) control the rate of addition of titrant as follows: Delivery of titrant will be incremental; after delivery of precisely a 0.100-mL increment (see 6.1.2), the delivery is stopped and a fixed time period of 90 s is allowed to pass before another 0.100-mL increment of titrant is delivered. This procedure is repeated until the titration is completed.
6.1.2 The precision of addition of the 0.100-mL increments of titrant must be 60.001 mL for automatic titrators. For manual buret, it should be 60.005 mL. A higher incremental precision is required for an automatic buret because the total volume to the end point is summed from the individual increments, whereas with a manual buret it is read from a scale.
6.2 Glass Indicating Electrode, pH 0 to 14, general purpose.
6.3 Reference Electrode, Silver/Silver Chloride (Ag/AgCl) reference electrode, filled with 1 M - 3 M LiCl in ethanol.
NOTE 4 - Certain alternative electrode-electrolyte combinations have been found to give satisfactory results although the precision using these alternatives has not been determined. Combination electrodes may be used provided they conform to 8.3 and have a sufficient fast response time.
6.4 Stirrer, Buret, Stand, Titration Vessel, as specified in Annex A1 are required. A typical cell assembly is shown in Fig. 1.
7. Reagents
7.1 Buffer, Nonaqueous Acid - Add 10 mL of buffer stock solution A (see 7.3) to 100 mL of titration solvent. Use within 1 h.
7.2 Buffer, Nonaqueous Base - Add 10 mL of buffer stock solution B (see 7.4) to 100 mL of titration solvent. Use within 1 h.
7.3 Buffer Stock Solution A - Accurately weigh 24.2 more or less 0.1 g of 2,4,6-trimethyl pyridine (g-collidine), and transfer to a 1-L volumetric flask containing 100 mL of anhydrous isopropyl alcohol. Using a 250-mL graduated cylinder, add to the flask, while continuously stirring its contents, 150/NHCl more or less 5 mL of 0.2 M alcoholic HCl solution (NHCl being the exact molarity of the HCl solution found by standardization). Dilute to the 1000-mL mark with anhydrous isopropyl alcohol, and mix thoroughly. Use within 2 weeks.
7.4 Buffer Stock Solution B - Accurately weigh 27.8 more or less 0.1 g of m-nitrophenol and transfer to a 1-L volumetric flask containing 100 mL of anhydrous isopropyl alcohol. Using a 250-mL graduated cylinder, add to the flask while continuously stirring its contents, 50/NKOH more or less 1 mL of 0.2 M alcoholic KOH solution. (NKOH being the exact molarity of the KOH solution found by standardization). Dilute to the 1000-mL mark with anhydrous isopropyl alcohol and mix thoroughly. Use within 2 weeks.
7.5 Chloroform, reagent grade. (Warning - Toxic and suspected carcinogen.)
7.6 Chromic Acid Solution - (Warning - Causes severe burns. Recognized carcinogen. Strong oxidizer.)
7.7 Hydrochloric Acid Solution, Standard Alcoholic (0.1 M) - Mix 9 mL of reagent grade hydrochloric acid (HCl, sp gr 1.19) (Warning - Toxic and corrosive), with 1 L of anhydrous isopropyl alcohol. Standardize frequently enough to detect normality changes of 0.0005 by potentiometric titration of approximately 8 mL (accurately measured) of the 0.1 M alcoholic KOH solution diluted with 125 mL CO2-free water.
7.8 Hydrochloric Acid Solution, Standard Alcoholic - (0.2 M) - Prepare and standardize as described in 7.7, but use 18 mL of HCl (sp gr 1.19) .
7.9 Lithium Chloride Electrolyte - Prepare a saturated solution of lithium chloride (LiCl) in isopropyl alcohol.
7.10 m-Nitrophenol, NO2C6H4OH, (Warning - Toxic), (mol weight 139.11), conforming to the following requirements:
7.10.1 Store the reagent in a brown glass bottle.
7.11 Potassium Hydroxide Solution, Standard Alcoholic (0.1 M) - Add 6 g of reagent grade potassium hydroxide (KOH) (Warning - Toxic and corrosive), to approximately 1 L of anhydrous isopropyl alcohol. Boil gently for 10 min to effect solution. Allow the solution to stand for 2 days and then filter the supernatant liquid through a fine sintered-glass funnel. Store the solution in a chemically resistant bottle. Dispense in a manner such that the solution is protected from atmospheric carbon dioxide (CO2) by means of a guard tube containing soda lime or soda non-fibrous silicate absorbent (Ascarite, Carbosorb, or Indicarb), and such that it does not come into contact with cork, rubber, or saponifiable stopcock grease. Standardize frequently enough to detect normality changes of 0.0005 by potentiometric titration of weighed quantities of potassium acid phthalate dissolved in CO2-free water.
7.12 Potassium Hydroxide Solution, Standard Alcoholic (0.2 M) - Prepare, store, and standardize as directed in 7.11, but use 12 to 13 g of KOH to approximately 1 L of anhydrous isopropyl alcohol.
7.13 Propanol-2-ol (Isopropyl Alcohol), Anhydrous, (less than 0.1 % H2O) (Warning - Flammable). If dry reagent cannot be procured, dry it by distillation through a multiple plate column, discarding the first 5 % of material distilling over and using the 95 % remaining. Also, drying can be accomplished using molecular sieves such as Linde Type 4A, by passing the solvent upward through a molecular sieve column using 1 part of molecular sieve per 10 parts of solvent. (Warning - It has been reported that, if not inhibited against it, propanol-2-ol can contain peroxides. When this occurs, an explosive mixture is possible when the storage vessel or other equipment such as a dispensing bottle, are near empty and approaching dryness.)
7.14 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.
7.14.1 Commercially available solutions may be used in place of laboratory preparations provided the solutions have been certified as equivalent.
7.14.2 Alternate volumes of solutions may be prepared provided the final solution concentration is equivalent.
7.15 Purity of Water - Unless otherwise indicated, references to water shall be understood to mean reagent water as defined by Type III of Specification D1193.
7.16 Titration Solvent - In a brown reagent bottle, add 30 mL of water to 1 L of isopropyl alcohol and mix thoroughly. Add 1 L each of toluene and chloroform and mix thoroughly.
7.17 Toluene, reagent grade. (Warning - Extremely flammable.)
7.18 2,4,6-Trimethyl Pyridine (g-Collidine), (CH3)3C5H2N, (Warning - Toxic), (mol weight 121.18) conforming to the following requirements:
7.18.1 Store the reagent over activated alumina and keep it in a brown glass bottle.