SENSITIVE FUSED-SILICA CAPILLARY GAS-CHROMATOGRAPHIC ASSAY USING ELECTRON-CAPTURE DETECTION FOR INDOMETHACIN IN OVINE FETAL FLUIDS

A sensitive gas chromatographic (GC) method with electron-capture detection (ECD) has been developed to quantitate indomethacin (IND) in plasma, urine, amniotic, and tracheal fluids obtained from the pregnant sheep model. IND and the internal standard, alpha-methylindomethacin (alpha-Me-IND) are extracted by a simple liquid-liquid extraction procedure using ethyl acetate and derivatized with N-methyl-N-(tert.-butyldimethylsilyl)trifluoroacetamide (MTBSTFA) at 60 degrees C for 50 min. The limit of quantitation (LOQ) is 1 ng/ml with a C.V. <10% and signal-to-noise ratio >10. Recoveries from all fluids were greater than 80%. Calibration curves were linear over the range of 1-32 ng/ml with a coefficient of determination (r(2)) >0.999. Inter- and intra-day coefficients of variation were <10% at concentrations of 2-32 ng/ml, and <20% at the LOQ, Applicability of the developed method is demonstrated for a pharmacokinetic study of IND samples collected following long-term infusion of IND in a chronically instrumented ovine fetus.