Mobile phase— Prepare a mixture of methanol and 0.05 M monobasic ammonium phosphate (64:36). Make adjustments if necessary (see System Suitability under Chromatography 621).

System suitability preparation— Proceed as directed in the Assay under Lorazepam Injection.

Standard solution— Prepare a solution in Mobile phase having known concentrations of about 3.2 µg each of USP Lorazepam Related Compound C RS and USP Lorazepam Related Compound D RS, and 0.16 µg of USP Lorazepam Related Compound B RS per mL.

Test solution— Transfer an accurately measured volume of Oral Concentrate, equivalent to about 4 mg of lorazepam, to a 25-mL volumetric flask, dilute with Mobile phase to volume, and mix to obtain a solution having a known concentration of about 0.16 mg per mL.

Chromatographic system— Proceed as directed in the Assay under Lorazepam Injection, except that the flow rate is 0.7 mL per minute.

Procedure— Separately inject equal volumes (about 20 µL) of the Standard solution and the Test solution into the chromatograph, record the chromatograms, and measure the responses of any peaks other than the lorazepam peak. Do not include as an impurity any peak observed in the chromatogram of the Test solution that has a retention time shorter than that of the lorazepam related compound D peak in the Standard solution. Calculate the percentages of lorazepam related compound B, lorazepam related compound C, and lorazepam related compound D taken by the formula: in which CS is the concentration, in µg per mL, of the corresponding component in the Standard solution; CU is the concentration, in µg per mL, of lorazepam in the Test solution; rU is the peak response of lorazepam related compound B, lorazepam related compound C, or lorazepam related compound D in the chromatogram obtained from the Test solution; and rS is the peak response of the corresponding component in the Standard solution. Not more than 0.1% of lorazepam related compound B is found; and not more than 4.0% for the sum of lorazepam related compound C and lorazepam related compound D is found.

Mobile phase— Prepare a mixture of water, acetonitrile, and glacial acetic acid (55:45:0.2). Make adjustments if necessary (see System Suitability under Chromatography 621).

System suitability preparation —Dissolve 10 mg each of Lorazepam and USP Lorazepam Related Compound E RS in 100 mL of methanol.

Standard preparation— Dissolve an accurately weighed quantity of USP Lorazepam RS in methanol, and dilute quantitatively, and stepwise if necessary, with methanol to obtain a solution having a known concentration of about 0.05 mg per mL.

Assay preparation— Transfer an accurately measured volume of Oral Concentrate, equivalent to 5 mg of lorazepam, to a 100-mL volumetric flask, and dilute with methanol to volume to obtain a solution containing about 0.05 mg of lorazepam per mL.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 254-nm detector and a 4-mm × 30-cm column that contains 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 standard deviation is not more than 2.0%. Chromatograph the System suitability preparation, and record the peak responses as directed for Procedure: the relative retention times are about 0.6 for lorazepam and 1.0 for lorazepam related compound E; and the resolution, R, between lorazepam and lorazepam related compound E is not less than 2.0.

Procedure— Separately inject equal volumes (about 20 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of lorazepam (C15H10Cl2N2O2) in the portion of Oral Concentrate taken by the formula: in which C is the concentration, in mg per mL, of USP Lorazepam RS in the Standard preparation; and rU and rS are the lorazepam peak responses obtained from the Assay preparation and the Standard preparation, respectively.