Assay for bretylium tosylate—
pH 3.1 Tetramethylammonium phosphate buffer, Mobile phase, Standard preparation, and Chromatographic system—
Proceed as directed in the
Assay under
Bretylium Tosylate Injection.
Assay preparation—
Transfer an accurately measured volume of Injection, equivalent to about 10 mg of bretylium tosylate, to a 50-mL volumetric flask, dilute with water to volume, and mix.
Procedure—
Separately inject equal volumes (about 20 µL) of the
Standard preparation and the
Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of bretylium tosylate (C
18H
24BrNO
3S) in each mL of the Injection taken by the formula:
50(C/V)(rU / rS),
in which
C is the concentration, in mg per mL, of
USP Bretylium Tosylate RS in the
Standard preparation; V is the volume, in mL, of Injection taken; and
rU and
rS are the bretylium peak responses from the
Assay preparation and the
Standard preparation, respectively.
Assay for dextrose—
Transfer an accurately measured volume of Injection, containing 2 to 5 g of dextrose, to a 100-mL volumetric flask. Add 0.2 mL of 6 N ammonium hydroxide, dilute with water to volume, and mix. Determine the angular rotation in a suitable polarimeter tube (see
Optical Rotation 
781
). Calculate the percentage (g per 100 mL) of dextrose (C
6H
12O
6·H
2O) in the portion of Injection taken by the formula:
(100/52.9)(198.17/180.16)AR,
in which 100 is the percentage; 52.9 is the midpoint of the specific rotation range for anhydrous dextrose, in degrees; 198.17 and 180.16 are the molecular weights for dextrose monohydrate and anhydrous dextrose, respectively;
A is 100 mm divided by the length of the polarimeter tube, in mm; and
R is the observed rotation, in degrees.
