Mobile phase ,Neutralized methanol,Diluent,Derivatizing reagent,Standard preparation,Resolution solution,and Chromatographic system—Proceed as directed in the Assayunder Monensin.

Assay preparation— Transfer about 5g of Premix,accurately weighed,to a 250-mLflask,add 200.0mLof Diluent,and shake by mechanical means for 1hour.Allow the solids to settle,and dilute an accurately measured volume of the clear supernatant quantitatively with Diluentto obtain a solution containing about 20µg of monensin per mL.

Procedure— Proceed as directed for Procedurein the Assayunder Monensin.Calculate the quantity,in mg,of monensin Ain each g of the Premix taken by the formula: in which Cis the concentration,in µg per mL,of monensin activity in the Standard preparation,based on the quantity of USP Monensin Sodium RStaken,its designated potency,in µg per mg,and the extent of dilution,Fis the designated percentage of monensin Ain USP Monensin Sodium RS,Dis the dilution factor used in preparing the Assay preparation,Wis the quantity,in g,of Premix taken to prepare the Assay preparation,and rUand rSare the monensin Apeak responses obtained from the Assay preparationand the Standard preparation,respectively.Calculate the quantity,in mg,of monensin Bin each g of the Premix taken by the same formula,except that rUis the monensin Bpeak response obtained from the Assay preparationand rSis the monensin Apeak response obtained from the Standard preparation.Calculate the quantity,in mg,of monensin C/Din each g of the Premix taken by the same formula,except that rUis the monensin C/Dpeak response obtained from the Assay preparation.Calculate the potency,in mg of monensin,in each g of the Premix taken by the formula: in which Ais the quantity,in mg,of monensin Ain each g of the Premix taken,as calculated above,and Bis the quantity,in mg,of monensin Bin each g of the Premix taken,and C/Dis the quantity,in mg,of monensin C/Din each g of Premix taken,as calculated above.