Subpart G—Chemical Tests for Nonantibiotic Active Ingredients

(a) Equipment—(1) Chromatography tank. A rectangular tank, approximately 9 × 9 × 3.5 inches with a glass solvent trough on the bottom. (2) Plates. Use 20 × 20 centimeter thin layer chromatography plates coated with Silica Gel G or equivalent to a thickness of 250 microns. (b) Developing solvent. Mix benzene and methanol in volumetric proportions of 90:10. (c) Preparation of spotting solutions— (1) Sample solution. Use the sample solution prepared as described in the section for the particular product to be tested. (2) Reference solution. Prepare a solution containing 0.5 milligram of iodochlorhydroxyquin U.S.P. reference standard per milliliter in acetone. (d) Procedure. Pour developing solvent into the glass trough on the bottom of the chromatography tank. Cover and seal the tank. Allow it to equilibrate for 1 hour. Spot a plate as follows: Apply approximately 10 microliters each of the sample solution and of the reference solution on a line 2.0 centimeters from the base of the silica gel plate and at intervals of not less than 2.0 centimeters. After all spots are thoroughly dry, place the silica gel plate directly into the glass trough of the chromatography tank. Cover and reseal the tank. Allow the solvent front to travel about 15 centimeters from the starting line, remove the plate from the tank, and allow to air dry. Examine under a strong source of ultraviolet light. The sample and standard are visible as dark spots. (e) Evaluation. Measure the distance the solvent front traveled from the starting line and the distance the spots are from the starting line. Calculate the Rf value by dividing the latter by the former. The sample and standard should have spots of corresponding Rf values (0.55 to 0.60). Subpart H—Tests for Specific Antibiotic Dosage Forms