The reliability of a solid-phase extraction system for the analysis of benzoylecgonine in urine.
Gas chromatographic-mass spectrometric (GC-MS) analysis for benzoylecgonine (BE), a metabolite of cocaine, requires an initial extraction from urine. Although liquid-liquid extraction methods are frequently used, solid-phase extraction (SPE) may be preferable for obtaining reliable results and clean chromatograms. We describe a 12-month study that evaluates the accuracy, precision, variability between analysts, variability between column lots, and cleanliness of BE extracts using SPE columns followed by GC-MS analysis. The overall mean for a control urine sample prepared at 150 ng/mL is 151 ng/mL (N = 293) with a standard deviation of 8.59 and a coefficient of variation (CV) of 5.7%. Within-run precision (measured as CV) at 75, 150, and 2000 ng/mL is 4.0, 1.8, and 0.8%, respectively. Mean results from 10 different analysts vary a maximum of 4.6% from the overall mean of 151 ng/mL, and the CV for 9 out of 10 analysts is 7.0% or less. The CV for the remaining analyst is 10.4%. Quantitative results from nine different lots of SPE columns fluctuate 3.3% from the overall mean of 151 ng/mL, and the CV varies from 3.5 to 6.2%. GC-MS chromatograms following SPE are significantly cleaner (i.e., reduced baseline signal and no interfering peaks) than those from two types of liquid-liquid extractions.
Jennison
T A
TA
Department of Pathology, University of Utah, Salt Lake City.
Jones
C W
CW
Wozniak
E
E
Urry
F M
FM
D002853:Chromatography, Liquid; D003042:Cocaine / Q000031:analogs & derivatives* / Q000652:urine; D005069:Evaluation Studies as Topic; D008401:Gas Chromatography-Mass Spectrometry; D006801:Humans; D009294:Narcotics / Q000652:urine*; D015203:Reproducibility of Results
D009294:Narcotics; C005618:benzoylecgonine; D003042:Cocaine