Screening for basic drugs in 2-mL urine samples by dual-plate overpressured layer chromatography and comparison with gas chromatography-mass spectrometry.

A dual-plate overpressured layer chromatography (OPLC) method was evaluated for broad-scale screening of basic drugs in 2-mL autopsy urine samples. Extraction was carried out by mixed-mode solid-phase extraction, and identification was based on automated comparison of corrected Rf values (hRfc) and in situ UV spectra with library values by dedicated software. The day-to-day precision of hRfc values was good in both OPLC1 and OPLC2 systems with median relative standard deviations of 2.4% and 3.4%, respectively. Both Rf and hRfc values were independent of the amount of analyte (0.5-10 microg) applied to the plate. Detection limits were determined for 47 drug substances in 2-mL urine samples, and they varied between 0.05 and 3.5 mg/L with a median of 1.0 mg/L. The performance of OPLC was evaluated by analyzing 30 autopsy urine samples by both OPLC and gas chromatography-mass spectrometry (GC-MS). The majority of findings by OPLC were in agreement with GC-MS. Some substances with low concentrations were not detected by OPLC, whereas GC-MS failed to detect a few polar substances. The OPLC method thus provides an alternative for current planar and column liquid chromatographic drug screening methods with the possibility of lowering detection limits by using a larger sample size.