Assay
TCA solution
Dissolve a quantity of trichloroacetic acid in water to obtain a 20% (w/v) solution.
Gold chloride solution
Dissolve a quantity of gold chloride in water to obtain a 0.5% (w/v) solution.
Blank
Use water.
Bromide standard stock solution
Dissolve an accurately weighed quantity of
USP Sodium Bromide RS in water to obtain a solution having a known concentration equivalent to about 20 mg of bromide per mL.
Standard preparations
Prepare four Standard preparation solutions of known concentrations of about 2.0 mg of bromide per mL, 1.0 mg of bromide per mL, 0.5 mg of bromide per mL, and 0.25 mg of bromide per mL by quantitatively diluting the Bromide standard stock solution with the appropriate volumes of water.
Assay preparation
Dilute Oral Solution, Veterinary quantitatively with water (1:99).
Procedure (see Spectrophotometry and Light Scattering
851
)
To 750-µL aliquots each of
Blank, the four
Standard preparations, and the
Assay preparation add 500 µL of
TCA solution and 250 µL of
Gold chloride solution. Mix on a vortex mixer, and immediately read the absorbance at 440 nm. Generate a standard curve of absorbance versus bromide concentration, correcting for the blank, and calculate the regression line and the regression coefficient. The test is considered valid if the square of the correlation coefficient of the regression curve (
r2) is not less than 0.99. Calculate the concentration, in mg per mL, of bromide (Br

) in the portion of Oral Solution, Veterinary taken by the formula:
100C
in which
C is the concentration, in mg per mL, of bromide in the
Assay preparation as calculated from the regression line.
USP32