§ 436.333 - Thin layer chromatographic identity test for moxalactam.

(a) Equipment—(1) Chromatography tank. A rectangular tank, approximately 23 centimeters long, 23 centimeters high, and 9 centimeters wide, equipped with a glass solvent trough in the bottom and a tight-fitting cover for the top. Line the inside walls of the tank with Whatman #3MM chromatographic paper or equivalent.

(2) Plates. Use a 20 x 20 centimeter thin layer chromotagraphy plate coated with silca gel G or equivalent to a thickness of 250 micrometers.

(b) Developing solvent. Mix ethyl acetate, glacial acetic acid, acetonitrile, and water in volumetric proportions of 42:14:14:18, respectively.

(c) Preparation of spotting solutions. Prepare solutions of the sample and working standard, each containing 10 milligrams per milliliter of moxalactam in distilled water.

(d) Procedure. Pour the developing solvent into the glass trough on the bottom of the tank and onto the paper lining the walls of the tank. Cover and seal the tank. Allow it to equilibrate for 1 hour. Prepare a plate as follows: On a line 2 centimeters from the base of the silica gel plate, and at intervals of 2 centimeters, spot 10 microliters each of the standard solution and the sample solution. After all spots are thoroughly dry, place the silica gel plate directly into the glass trough. Cover and seal the tank. Allow the solvent front to travel about 15 centimeters from the starting line. Remove the plate from the tank and air dry. Expose the plate to iodine vapors for 40 minutes. Immediately circumscribe all spots using a suitable marker.

(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 and intensity.