Identification—
Apply separately a volume of Injection equivalent to 20µg of gentamicin and the same volume of a similar preparation of
USP Gentamicin Sulfate RSto a suitable thin-layer chromatographic plate (see
Chromatography á621ñ)coated with a 0.25-mm layer of chromatographic silica gel having an average pore size of 6nm.
[NOTE—Dilute the Injection with water,if necessary,to obtain a test solution containing 1000µg of gentamicin per mL.Where the Injection contains less than 1000µg per mL,apply a volume of it,equivalent to 20µg of gentamicin,to the chromatographic plate,in separate portions of not more than 20µLeach,each application being allowed to dry before the next is applied.
]Place the plate in a suitable chromatographic chamber,and develop the chromatogram in a solvent system consisting of the lower phase of a mixture of chloroform,methanol,and ammonium hydroxide (20:13:10)until the solvent front has moved about three-fourths of the length of the plate.Remove the plate from the chamber,air-dry,and expose the plate to vapors of iodine in a detection jar containing iodine crystals:the intensities and
RFvalues of the three principal spots obtained from the test solution correspond to those obtained from the Standard solution.
Assay—
Proceed as directed under
Antibiotics—Microbial Assays á81ñ,using an accurately measured volume of Injection diluted quantitatively and stepwise with
Buffer No.3to yield a
Test Dilutionhaving a concentration assumed to be equal to the median dose level of the Standard (0.1µg of gentamicin per mL).