Medium: water; 900 mL.

Apparatus 2: 50 rpm.

Time: 45 minutes.

Procedure— Determine the amount of C11H15NO5 dissolved, employing the procedure set forth in the Assay, making any necessary modifications.

Tolerances— Not less than 75% (Q) of the labeled amount of C11H15NO5 is dissolved in 45 minutes.

(Official January 1, 2007)

pH 4.5 Buffer solution, Mobile phase, and Chromatographic system— Proceed as directed in the Assay under Methocarbamol Injection.

Internal standard solution— Prepare a solution of caffeine in methanol containing about 3 mg per mL.

Standard preparation— Transfer about 100 mg of USP Methocarbamol RS, accurately weighed, to a 100-mL volumetric flask. Dissolve in about 50 mL of pH 4.5 Buffer solution and 25 mL of methanol. Add 5.0 mL of Internal standard solution, dilute with pH 4.5 Buffer solution to volume, and mix.

Assay preparation— Weigh and powder not less than 10 Tablets. Transfer an accurately weighed portion of the powder, equivalent to 100 mg of methocarbamol, to a 100-mL volumetric flask. Add about 50 mL of pH 4.5 Buffer solution, 25 mL of methanol, and 5.0 mL of Internal standard solution. Shake vigorously for 10 minutes, dilute with pH 4.5 Buffer solution to volume, and mix. Filter, discarding the first 20 mL of the filtrate.

Procedure— Proceed as directed for Procedure in the Assay under Methocarbamol Injection. Calculate the quantity, in mg, of methocarbamol (C11H15NO5) in the portion of Tablets taken by the formula: in which C is the concentration, in mg per mL, of USP Methocarbamol RS in the Standard preparation; and RU and RS are the peak response ratios of methocarbamol and caffeine obtained from the Assay preparation and the Standard preparation, respectively.