Solution A— Transfer 0.55g of sodium 1-heptanesulfonate to a 1000-mLvolumetric flask,dissolve in and dilute with water to volume,and mix.

Mobile phase— Transfer 10g of monobasic potassium phosphate to a 1000-mLbeaker,dissolve in 300mLof Solution A,add 250mLof methanol,followed by another 300mLof Solution A,and mix.Adjust the mixture with phosphoric acid to a pHof 2.2.Transfer the whole mixture to a 1000-mLvolumetric flask,dilute with Solution Ato volume,and mix.Filter and degas.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Internal standard solution— Prepare a solution of methionine in water containing 1.25mg per mL.

Standard preparation— Dissolve an accurately weighed quantity of USP Aminocaproic Acid RSin water to obtain a Stock solutionhaving a known concentration of 12.5mg per mL.Transfer 5.0mLof the Stock solutionto a 100-mLvolumetric flask,add 2.0mLof the Internal standard solution,dilute with water to volume,and mix.

Assay preparation— Transfer an accurately weighed quantity of 1.25g of Aminocaproic Acid to a 100-mLvolumetric flask,dissolve in and dilute with water to volume,and mix.Transfer 5.0mLof this solution to a 100-mLvolumetric flask,add 2.0mLof Internal standard solution,dilute with water to volume,and mix.

Chromatographic system(see Chromatography á621ñ)— The liquid chromatograph is equipped with a 210-nm detector and a 4.6-mm ×15-cm column that contains packing L1and is maintained at 30.The flow rate is about 0.7mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the relative retention times are about 0.76for aminocaproic acid and 1.0for methionine;the resolution,R,between aminocaproic acid and methionine is not less than 2.0;and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 20µL)of the Standard preparationand the Assay preparationinto the chromatograph,and allow the Assay preparationto elute for not less than two times the retention time of aminocaproic acid.Record the chromatograms,and measure all the peak responses.Calculate the quantity,in mg,of C6H13NO2in the portion of Aminocaproic Acid taken by the formula: in which Cis the concentration,in mg per mL,of USP Aminocaproic Acid RSin the Standard preparation;and RUand RSare the ratios of the aminocaproic acid peak response to the internal standard peak response obtained from the Assay preparationand the Standard preparation,respectively.