Medium: water;900mL.

Apparatus 2: 50rpm.

Time: 45minutes.

Procedure— Determine the amount of C11H15NO5dissolved,employing the procedure set forth in the Assay,making any necessary modifications.

Tolerances— Not less than 75%(Q)of the labeled amount of C11H15NO5is dissolved in 45minutes.

pH4.5Buffer solution,Mobile phase,andChromatographic system— Proceed as directed in the Assayunder Methocarbamol Injection.

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

Standard preparation— Transfer about 100mg of USP Methocarbamol RS,accurately weighed,to a 100-mLvolumetric flask.Dissolve in about 50mLof pH4.5Buffer solutionand 25mLof methanol.Add 5.0mLof Internal standard solution,dilute with pH4.5Buffer solutionto volume,and mix.

Assay preparation— Weigh and powder not less than 10Tablets.Transfer an accurately weighed portion of the powder,equivalent to 100mg of methocarbamol,to a 100-mLvolumetric flask.Add about 50mLof pH4.5Buffer solution,25mLof methanol,and 5.0mLof Internal standard solution.Shake vigorously for 10minutes,dilute with pH4.5Buffer solutionto volume,and mix.Filter,discarding the first 20mLof the filtrate.

Procedure— Proceed as directed for Procedurein the Assayunder Methocarbamol Injection.Calculate the quantity,in mg,of methocarbamol (C11H15NO5)in the portion of Tablets taken by the formula: in which Cis the concentration,in mg per mL,of USP Methocarbamol RSin the Standard preparation;and RUand RSare the peak response ratios of methocarbamol and caffeine obtained from the Assay preparationand the Standard preparation,respectively.