Packaging and storage—
Preserve in well-closed containers.
Identification—
Solution:
40 µg per mL.
Medium:
water.
C:
Dissolve 100 mg in 50 mL of water: a 10-mL portion of the solution responds to the tests for
Chloride 
191
, except that a turbidity is produced, rather than a curdy white precipitate, when the silver nitrate TS is added.
Acidity—
Dissolve 500 mg, accurately weighed, in 50 mL of water, add phenolphthalein TS, and titrate with 0.020 N sodium hydroxide: not more than 2.5 mL is required for neutralization.
Heavy metals, Method II 231:
0.002%.
Pyridine—
Dissolve 1 g in 10 mL of sodium hydroxide solution (1 in 10) without heating: the odor of pyridine is not immediately perceptible.
Organic volatile impurities, Method V 467:
meets the requirements.
Assay—
Transfer about 200 mg of Cetylpyridinium Chloride, accurately weighed, to a glass-stoppered, 250-mL graduated cylinder containing 75 mL of water. Add 10 mL of chloroform, 0.4 mL of bromophenol blue solution (1 in 2000), and 5 mL of a freshly prepared solution of sodium bicarbonate (4.2 in 1000), and titrate with 0.02 M sodium tetraphenylboron VS until the blue color disappears from the chloroform layer. Add the last portions of the sodium tetraphenylboron solution dropwise, agitating vigorously after each addition. Each mL of 0.02 M sodium tetraphenylboron is equivalent to 6.800 mg of C21H38ClN.
;)
and 84