Precision and accuracy in the quantitation of carboxytetrahydrocannibinol by isotope dilution gas chromatography/mass spectrometry.
The classical definitions of method detection limit (MDL) and limit of quantitation (LOQ) are redefined using calibration curve regression analysis. Traditional ways of determining these parameters provide scant information on the daily precision of the analysis at all concentration levels. These parameters are time consuming to acquire and hold only for the moment of acquisition. It is illustrated, with experimental data, using isotope dilution analyses of THC-COOH, a marijuana metabolite, that not only can MDL and LOQ be obtained directly from the calibration curve, but confidence intervals for the calibration curve can also be obtained, which define the precision of the analyses at all levels calibrated. If calibration and analyses of unknowns take place simultaneously, then an MDL and confidence intervals that are relevant to data acquisition are obtained. Confidence intervals at particular analyte concentrations of interest were of greater value than the MDL and LOQ in evaluation of the analytical method. The parameter from the calibration curve is defined as the calibrated quantitation limit.
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Diagnostic Products Corporation, West Los Angeles, California 90045.
D013759:Dronabinol / Q000031:analogs & derivatives* / Q000032:analysis; D008401:Gas Chromatography-Mass Spectrometry; D007202:Indicators and Reagents; D012044:Regression Analysis
D007202:Indicators and Reagents; D013759:Dronabinol; C025351:delta(9)-tetrahydrocannabinolic acid