Identification—
Mix the contents of 1 Capsule with water to obtain a concentration of about 3 mg of cephalexin per mL, and filter (test solution). Place a suitable thin-layer chromatographic plate (see
Chromatography 
621
) coated with a 0.25-mm layer of binder-free silica gel in a chamber containing a mixture of
n-hexane and tetradecane (95:5) to a depth of about 1 cm, allow the solvent front to move the length of the plate, remove the plate from the chamber, and allow the solvent to evaporate. On this plate apply 10 µL each of the test solution and a Standard solution containing 3 mg of
USP Cephalexin RS per mL. Allow the spots to dry, and develop the chromatogram in a solvent system consisting of a mixture of 0.1
M citric acid, 0.1
M dibasic sodium phosphate, and a 1 in 15 solution of ninhydrin in acetone (60:40:1.5) until the solvent front has moved about three-fourths of the length of the plate. Remove the plate from the developing chamber, mark the solvent front, dry the plate for 10 minutes at 110
, and examine the chromatogram: the
RF value of the principal spot obtained from the test solution corresponds to that obtained from the Standard solution.
Dissolution 711—
Medium:
water; 900 mL.
Apparatus 1:
100 rpm.
Time:
30 minutes.
Procedure—
Determine the amount of C
16H
17N
3O
4S dissolved from the UV absorbances at the wavelength of maximum absorbance at about 262 nm of a filtered portion of the solution under test, suitably diluted with
Dissolution Medium, if necessary, to a concentration of about 20 µg per mL, in comparison with a Standard solution having a known concentration of
USP Cephalexin RS in the same medium.
Tolerances—
Not less than 80% (Q) of the labeled amount of C16H17N3O4S is dissolved in 30 minutes.
Assay—
Mobile phase
,
Internal standard solution,
Standard preparation, and
Chromatographic system—Prepare as directed in the
Assay under
Cephalexin.
Assay preparation—
Remove, as completely as possible, the contents of not less than 20 Capsules, and weigh accurately. Mix the combined contents, and transfer an accurately weighed quantity, equivalent to about 500 mg of cephalexin, to a 500-mL volumetric flask, add water to volume, and mix. Sonicate, if necessary, to assure complete dissolution of the cephalexin. Filter, if necessary, to obtain a clear solution. Transfer 10.0 mL of this solution to a 50-mL, glass-stoppered flask, add 15.0 mL of Internal standard solution, mix, and filter.
Procedure—
Proceed as directed for
Procedure in the
Assay under
Cephalexin. Calculate the quantity, in mg, of C
16H
17N
3O
4S in the portion of Capsules taken by the formula:
0.5CP(RU / RS),
in which the terms are as defined therein.
