Specific rotation 
781S
:
between +124
and +134
, calculated on the dried and sodium bicarbonate-free basis.
Test solution:
a known amount of specimen, equivalent to about 50 mg of cephalothin, per mL, in water.
Content of sodium bicarbonate (if present)—
Dissolve about 1 g of it, accurately weighed, in 50 mL of water. Add methyl orange TS, and titrate with 0.1 N sulfuric acid VS. Each mL of 0.1 N sulfuric acid is equivalent to 8.401 mg of NaHCO
3. Calculate the percentage of sodium bicarbonate, and use the value obtained to calculate the
Specific rotation on the dried and sodium bicarbonate-free basis.
Assay—
Mobile phase
,
Resolution solution, and
Chromatographic system—Proceed as directed in the
Assay under
Cephalothin Sodium.
Standard preparation—
Dissolve a suitable quantity of
USP Cephalothin Sodium RS, accurately weighed, in
Mobile phase to obtain a solution having a known concentration of about 1 mg of cephalothin per mL.
Assay preparation 1
(where it is represented as being in a single-dose container)—Constitute Cephalothin for Injection in a volume of water, accurately measured, corresponding to the volume of solvent specified in the labeling. Withdraw all of the withdrawable contents, using a suitable hypodermic needle and syringe, and dilute quantitatively with Mobile phase to obtain a solution having a concentration of about 1 mg of cephalothin per mL.
Assay preparation 2
(where the label states the quantity of cephalothin in a given volume of constituted solution)—Constitute 1 container of Cephalothin for Injection in a volume of water, accurately measured, corresponding to the volume of solvent specified in the labeling. Dilute an accurately measured portion of the constituted solution quantitatively with Mobile phase to obtain a solution having a concentration of about 1 mg of cephalothin per mL.
Procedure—
Proceed as directed in the
Assay under
Cephalothin Sodium. Calculate the quantity, in mg, of cephalothin (C
16H
16N
2O
6S
2) in the container, and in the portion of constituted solution taken by the formula:
(L / D)(CP / 1000)(rU / rS),
in which
L is the labeled quantity of cephalothin in the container, or in the volume of constituted solution taken;
D is the concentration, in mg per mL, of cephalothin in
Assay preparation 1 or in
Assay preparation 2, on the basis of the labeled quantity in the container, or in the portion of constituted solution taken, respectively, and the extent of dilution; and the other terms are as defined therein. Where the test for
Uniformity of dosage units has been performed using the
Procedure for content uniformity, use the average of these determinations as the
Assay value.
