Identification, Infrared Absorption 
197M
—
Obtain the test specimen as follows. Transfer a quantity of powdered Tablets, equivalent to about 120 mg of guanethidine monosulfate, to a glass-stoppered flask, add 20 mL of water, shake by mechanical means for 30 minutes, and filter, discarding the first few mL of the filtrate. Transfer 10 mL of the filtrate to a separator, add 2 mL of 0.1 N sodium hydroxide and 2 mL of a saturated solution of picric acid in 0.1 N sodium hydroxide, and mix. Extract with 20 mL of chloroform, filter the chloroform extract through cotton, and collect in a beaker. Evaporate the chloroform extract with the aid of a stream of nitrogen to dryness.
Dissolution 711—
Medium:
water; 500 mL.
Apparatus 1:
100 rpm.
Time:
45 minutes.
Procedure—
Determine the amount of (C
10H
22N
4)
2·H
2SO
4 dissolved, employing the procedure set forth in the
Assay and making any necessary modifications.
Tolerances—
Not less than 75% (Q) of the labeled amount of (C10H22N4)2·H2SO4 is dissolved in 45 minutes.
Assay—
Borate solution—
Transfer 12.4 g of boric acid to a 1000-mL volumetric flask, dissolve in 100 mL of 1.0 N sodium hydroxide, dilute with water to volume, and mix.
Borate buffer—
Mix 400 mL of Borate solution with 600 mL of 0.1 N sodium hydroxide, and adjust with 1.0 N sodium hydroxide or 1.0 N hydrochloric acid to a pH of 12.3 ± 0.1.
Picrate reagent—
Transfer 15 g of picric acid to a 1000-mL volumetric flask, dissolve in 750 mL of 0.1 N sodium hydroxide, dilute with water to volume, and mix.
Assay preparation—
Finely powder not fewer than 20 Tablets. Transfer an accurately weighed portion of the powder, equivalent to about 50 mg of guanethidine sulfate, to a 200-mL volumetric flask, add 150 mL of 0.1 N sulfuric acid, shake by mechanical means for 30 minutes, dilute with 0.1 N sulfuric acid to volume, and mix. Filter, and discard the first 25 mL of the filtrate.
Procedure—
Pipet 5 mL each of the
Standard preparation and the
Assay preparation into separate 125-mL separators. To each separator add 20 mL of
Borate buffer and 20 mL of
Picrate reagent. Extract with three 20-mL portions of chloroform, filtering the extracts through chloroform-prerinsed cotton, and collect the extracts in low-actinic 100-mL volumetric flasks. Rinse the cotton with 20 mL of chloroform, adding the rinsings to the volumetric flasks, dilute with chloroform to volume, and mix. Concomitantly determine the absorbances of the solutions at the wavelength of maximum absorbance at about 412 nm, with a suitable spectrophotometer, using chloroform as the blank. Calculate the quantity, in mg, of guanethidine sulfate [(C
10H
22N
4)
2·H
2SO
4] in the portion of Tablets taken by the formula:
(247.35 / 296.39)(200)(C)(AU / AS),
in which 247.35 is one-half the molecular weight of guanethidine sulfate; 296.39 is the molecular weight of guanethidine monosulfate;
C is the concentration, in mg per mL, of
USP Guanethidine Monosulfate RS in the
Standard preparation; and
AU and
AS are the absorbances of the solutions from the
Assay preparation and the
Standard preparation, respectively.
