GAS-CHROMATOGRAPHY WITH SURFACE-IONIZATION DETECTION - A HIGHLY SENSITIVE METHOD FOR DETERMINING UNDERIVATIZED CODEINE AND DIHYDROCODEINE IN BODY-FLUIDS

Underivatized codeine and dihydrocodeine in human plasma and urine hav e been determined with a high degree of accuracy by capillary gas chro matography (GC) with surface ionization detection (SID). The drugs wer e extracted with the aid of Sep-Pak C-18 cartridges. Recovery of both drugs was greater than or equal to 90%. The calibration curves obtaine d with dimemorfan as an internal standard showed linearity in the rang e 4.5-72.3 and 3.0-75.5 ng/ml of plasma for codeine and dihydrocodeine , respectively. The detection limit was about 100 pg on column (2.5 ng /ml sample). Codeine was determined quantitatively in plasma and urine obtained from a volunteer who had received 10 mg codeine phosphate or ally 3 h before the sampling: the levels were found to be 14.1 and 142 ng/ml, respectively. The present GC-SID method has been compared care fully with GC-NPD (nitrogen-phosphorus detection) using the same extra cts; the sensitivity of GC-SID was more than ten times greater than th at of GC-NPD, with background noise correspondingly lower.