Identification—
B:
Finely powder a quantity of Tablets, equivalent to about 500 mg of probenecid, triturate the powder with alcohol, and filter. Evaporate the filtrate to about 20 mL, cool, acidify with hydrochloric acid until acid to litmus, remove the crystals by filtration, and recrystallize from diluted alcohol: the probenecid so obtained melts between 196
and 200
, as determined by the method for
Class Ia under
Melting Range or Temperature 
741
, and responds to
Identification test
A under
Probenecid.
Dissolution 711—
Medium:
simulated intestinal fluid TS, prepared without pancreatin, pH 7.5 ± 0.1; 900 mL.
Apparatus 2:
75 rpm.
Time:
30 minutes.
Procedure—
Determine the amount of C
13H
19NO
4S dissolved by employing UV absorption at the wavelength of maximum absorbance at about 244 nm on filtered portions of the solution under test, suitably diluted with 0.1 N sodium hydroxide, if necessary, in comparison with a Standard solution having a known concentration of
USP Probenecid RS.
Tolerances—
Not less than 80% (Q) of the labeled amount of C13H19NO4S is dissolved in 30 minutes.
Assay—
Weigh and finely powder not less than 20 Tablets. Weigh accurately a portion of the powder, equivalent to about 100 mg of probenecid, and transfer to a 250-mL volumetric flask. Add chloroform to volume, and mix. Filter a portion of the chloroform solution, discarding the first 20 to 25 mL of the filtrate, and pipet 5 mL of the filtrate into a 125-mL separator containing 10 mL of chloroform. Extract the chloroform layer with four 15-mL portions of sodium carbonate solution (1 in 100). Render the combined extracts distinctly acid with 5 N hydrochloric acid, and extract with four 20-mL portions of chloroform, filtering each extract through a small pledget of cotton into a 100-mL volumetric flask. Wash the cotton filter with 10 mL of chloroform, add chloroform to volume, and mix. Dissolve an accurately weighed quantity of
USP Probenecid RS in chloroform, and dilute quantitatively and stepwise with chloroform to obtain a Standard solution having a known concentration of about 20 µg per mL. Concomitantly determine the absorbances of both solutions in 1-cm cells at the wavelength of maximum absorbance at about 257 nm, with a suitable spectrophotometer, using chloroform as the blank. Calculate the quantity, in mg, of C
13H
19NO
4S in the portion of Tablets taken by the formula:
5C(AU / AS),
in which
C is the concentration, in µg per mL, of
USP Probenecid RS in the Standard solution; and
AU and
AS are the absorbances of the solution from the Tablets and the Standard solution, respectively.
