Determination of isoxsuprine in human plasma by gas chromatography with electron capture detection

A rapid and sensitive gas chromatographic method for the determination of the beta-adrenergic agent isoxsuprine in human plasma has been developed. The procedure involves the extraction of the drug with ether and an internal standard (propranolol) from plasma at alkaline pH, solvent evaporation, and the formation of a tri-trifluoroacetyl derivative by reaction with trifluoroacetic anhydride in ethyl acetate. Analyses were carried out by gas-liquid chromatography on a 3% OV-17 column using an electron capture detector. The minimum detectable amount of isoxsuprine was 0.5 ng/ml of plasma and the electron capture detector response was tested to be linear (r2 greater than 0.999) between 0.5 and 20 ng/ml. No interferences from endogenous substances were found. Precision of the method was found to be 9.9, and 6.1% coefficient of variation at 1 ng/ml and 10 ng/ml of plasma, respectively. Determination of isoxsuprine at the nanogram level in cord plasma samples from newborns at the time of the delivery was possible using the described procedure.