Packaging and storage—
Preserve in well-closed containers.
Identification—
Solution:
10 µg per mL.
Medium:
0.001 N sodium hydroxide.
B:
Dissolve about 400 mg in 10 mL of water, add 1 mL of 3 N hydrochloric acid, filter, and wash the precipitate with two 5-mL portions of cold water. Recrystallize from alcohol the precipitate so obtained, and dry at 110
for 1 hour: the
p-aminobenzoic acid so obtained melts between 186
and 189
.
C:
A solution (1 in 100) meets the requirements of the flame test for
Potassium 
191
.
pH 791:
between 8.0 and 9.0, in a solution (1 in 20).
Volatile diazotizable substances—
Standard preparation—
Dissolve 10 mg of p-toluidine in 5 mL of methanol in a 100-mL volumetric flask, add water to volume, and mix. Transfer 1 mL to a 100-mL volumetric flask, dilute with water to volume, and mix.
Test preparation—
Transfer 5.0 g of Aminobenzoate Potassium to a suitable flask, and add a volume of 1.25 N sodium hydroxide that is just sufficient to dissolve the test specimen and to render the solution just alkaline to
phenolphthalein TS. Dilute with water to 50 mL, and steam-distill the solution, collecting about 95 mL of the distillate in a 100-mL volumetric flask. Add water to volume, and mix.
Procedure—
Transfer 20.0-mL portions of the Standard preparation and the Test preparation to separate 100-mL beakers, and transfer 20.0 mL of water to a third 100-mL beaker to provide the blank. Treat each as follows. Add 5.0 mL of 1 N hydrochloric acid, and cool in an ice bath. Add 2.0 mL of 0.1 M sodium nitrite dropwise, with stirring, allow to stand for 5 minutes for the diazotization reaction to be complete, add quickly to 10.0 mL of a cold solution of guaiacol (freshly prepared by dissolving 0.20 g of guaiacol in 100 mL of 1 N sodium hydroxide), mix, and allow to stand for 30 minutes. Concomitantly determine the absorbances of the solutions at the wavelength of maximum absorbance at about 405 nm, with a suitable spectrophotometer, using the blank to set the instrument: the absorbance of the solution obtained from the Test preparation does not exceed that of the solution obtained from the Standard preparation, corresponding to not more than 0.002% of volatile diazotizable substances, as p-toluidine.
Chloride 221—
A 1.4-g portion shows no more chloride than corresponds to 0.4 mL of 0.020 N hydrochloric acid (0.02%).
Sulfate 221—
A 1.4-g portion shows no more sulfate than corresponds to 0.3 mL of 0.020 N sulfuric acid (0.02%).
Heavy metals, Method II 231:
0.002%.
Assay—
Transfer about 500 mg of Aminobenzoate Potassium, accurately weighed, to a suitable vessel, add 25 mL of water and 25 mL of 3 N hydrochloric acid, mix, and cool in an ice bath. Titrate with 0.1 M sodium nitrite VS, determining the endpoint potentiometrically, using a calomel-platinum electrode system. Each mL of 0.1 M sodium nitrite is equivalent to 17.52 mg of C7H6KNO2.
