Simultaneous measurement of flurbiprofen, ibuprofen, and ketoprofen enantiomer concentrations in plasma using L-leucinamide as the chiral coupling component

A high performance liquid chromatographic method was developed for the quantitation of the R- and S- enantiomers of 2-arylpropionic acid namely flurbiprofen, ibuprofen and ketoprofen, in plasma. The procedure involved extraction of drugs and internal standard from acidified plasma into dichloromethane. After evaporation of the organic layer, the compounds were derivatized with L-leucinamide after addition of ethyl chloroformate as the coupling reagent. The former diastereoisomeric amides were chromatographied at ambient temperature on a reversed phase column using 0.06M KH2PO4 - acetonitrile - triethylamine (51:49:0.1) as the mobile phase pumped at a flow rate of 1.8 ml/min. This assay allowed determination of 0.1 mu g/ml of both R- and S- enantiomers with an acceptable precision (maximum coefficient of variation of 7.5%) using a 0.5-ml plasma sample.