Impact of biological matrix, drug concentration, and method of isolation on detectability and variability of retention index values in gas chromatography.

The retention indices of eight basic and neutral drugs extracted from plasma, blood, or liver homogenate by six different methods were calculated using temperature-programmed gas chromatography on OV-1 and SE-30 columns. Two concentrations were applied: 1 and 50 mg/L, respectively. The type of extraction had great influence on recovery and analytical background. The retention indices tended to be slightly concentration-dependent in that they were somewhat lower at higher drug concentration. Neither the biological sample nor the type of extraction exerted significant influence on scatter and mean value of the retention indices.