pH 4.3 sodium phosphate buffer— Dissolve 13.8 g of monobasic sodium phosphate in 900 mL of water, adjust with phosphoric acid or 10 N sodium hydroxide to a pH of 4.3 ± 0.1, dilute with water to make 1000 mL, and mix.

Mobile phase— Prepare a suitable mixture of pH 4.3 sodium phosphate buffer and acetonitrile (95:5), and pass through a membrane filter of 0.5-µm or finer porosity. Make adjustments if necessary (see System Suitability under Chromatography 621).

pH 6.4 sodium phosphate buffer— Dissolve 6.9 g of monobasic sodium phosphate in 900 mL of water, adjust with 10 N sodium hydroxide to a pH of 6.4 ± 0.1, dilute with water to make 1000 mL, and mix.

Clavulanate lithium stock standard solution— Dissolve an accurately weighed quantity of USP Clavulanate Lithium RS in pH 6.4 sodium phosphate buffer to obtain a solution having a known concentration of about 0.6 mg per mL.

Standard preparation— Transfer about 100 mg of USP Ticarcillin Monosodium Monohydrate RS, accurately weighed, to a 100-mL volumetric flask, add 150/J mL of Clavulanate lithium stock standard solution, accurately measured, J being the ratio of the labeled amount, in mg, of ticarcillin to the labeled amount, in mg, of clavulanic acid in the Ticarcillin Disodium and Clavulanic Acid for Injection, dilute with pH 6.4 sodium phosphate buffer to volume, and mix.

Assay preparation— Dissolve the contents of 1 container of Ticarcillin and Clavulanic Acid for Injection in a volume of water, accurately measured, corresponding to the volume of solvent specified in the labeling. Using a suitable hypodermic needle and syringe, remove all of the withdrawable contents from the container, and dilute quantitatively and stepwise with pH 6.4 sodium phosphate buffer to obtain a solution having a concentration of about 0.9 mg of ticarcillin (C15H16N2O6S2) per mL.

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 220-nm detector and a 4-mm × 30-cm column that contains 3- to 10-µm packing L1. The flow rate is about 2 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the relative retention times are about 0.2 for clavulanic acid and 1.0 for ticarcillin; the column efficiency determined from the analyte peaks is not less than 1000 theoretical plates; the tailing factors for the analyte peaks are not more than 2.0; the resolution, R, between the ticarcillin and clavulanic acid peaks is not less than 5.0; and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 20 µL) of the Standard preparation and the Assay preparations into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of ticarcillin (C15H16N2O6S2) in the container of Ticarcillin and Clavulanic Acid for Injection taken by the formula: in which L is the labeled quantity, in mg, of ticarcillin in the container; D is the concentration, in mg per mL, of ticarcillin in the Assay preparation on the basis of the labeled quantity of ticarcillin in the container and the extent of dilution; C is the concentration, in mg per mL, of USP Ticarcillin Monosodium Monohydrate RS in the Standard preparation; P is the designated potency, in µg of ticarcillin per mg, of USP Ticarcillin Monosodium Monohydrate RS; and rU and rS are the ticarcillin peak responses obtained from the Assay preparation and the Standard preparation, respectively.

(L / D)(CP / 1000)(rU / rS)