Determination of felodipine in plasma by capillary gas chromatography with electron capture detection

Felodipine in plasma was extracted with toluene and determined by automated capillary gas chromatography with electron capture detection. Undesirable oxidation of the dihydropyridine derivative in the injector and in the column was avoided by the use of glass materials with the inner surfaces treated by high-temperature silylation. The day-to-day reproducibility of the method was represented by a relative standard deviation (RSD) of 5% for a felodipine concentration of 25 nmol/l. The minimum determinable concentration (giving better than 15% RSD) was 1-2 nmol/l (0.4-0.8 ng/ml).