Identification—
B:
Dissolve 2.5 mg in 10 mL of water. Add 2 mL of a solution prepared by dissolving 500 mg of 1-naphthol, 3 g of sodium hydroxide, and 8 g of sodium carbonate in water to make 50 mL, and 1 mL of a solution of 2,3-butanedione (1 in 2000). Allow to stand at room temperature: an intense, pinkish-red color develops.
Assay—
Sodium nitroferricyanide–potassium ferricyanide solution—
Dissolve 1 g of sodium nitroferricyanide and 1 g of potassium ferricyanide in water to make 100 mL, and mix.
Standard preparation—
Dissolve a suitable quantity of
USP Guanethidine Monosulfate RS, accurately weighed, in 1 N sulfuric acid to obtain a solution having a known concentration of about 1 mg per mL.
Assay preparation—
Transfer about 50 mg of Guanethidine Monosulfate, accurately weighed, to a 50-mL volumetric flask, dissolve in 1 N sulfuric acid, add 1 N sulfuric acid to volume, and mix.
Procedure—
Pipet 2 mL each of the
Assay preparation and the
Standard preparation, and 2 mL of 1 N sulfuric acid to provide the blank, into separate glass-stoppered, 40-mL centrifuge tubes. Add 10.0 mL of water to each tube, and mix. To each tube add 10.0 mL of
Sodium nitroferricyanide–potassium ferricyanide solution, mix, add 4.0 mL of 1 N sodium hydroxide, mix, and allow to stand for 20 minutes, accurately timed. Concomitantly determine the absorbances of both solutions in 1-cm cells against the blank at the wavelength of maximum absorbance at about 500 nm, with a suitable spectrophotometer. Calculate the quantity, in mg, of C
10H
22N
4·H
2SO
4 in the Guanethidine Monosulfate taken by the formula:
50C(AU / AS),
in which
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.
;)
791
:
between 4.7 and 5.7, in a solution containing 20 mg per mL.
to constant weight: it loses not more than 0.5% of its weight.