Reference measurement procedure for Δ9-tetrahydrocannabinol in serum
An isotope dilution gas chromatography/mass spectrometry (ID-GC/MS) reference measurement procedure for Δ9-tetrahydrocannabinol (THC) in serum was developed and validated. The method complies with the concept of a ratio primary reference measurement procedure. The uncertainty was determined for two concentrations of THC in serum (1 ng/mL and 2.4 ng/mL). The calculation procedure is based on the Guide to the Expression of Uncertainty in Measurement (GUM). The relative expanded uncertainty was found to be less than 2% for both concentration levels, corresponding to a 95% confidence interval. For the reference method, it was shown that the measurement of THC within the concentration range covered by the current threshold values is very accurate. The method has the potential to provide traceability for the methods used in practical forensics.
Development and evaluation of a candidate reference measurement procedure for the determination of progesterone in human serum using isotope-dilution liquid chromatography/tandem mass spectrometry.
Progesterone is a steroid hormone that is involved in regulating female reproductive processes. Its concentration in blood is measured to determine ovarian function. A candidate reference measurement procedure for progesterone in human serum involving isotope dilution coupled with liquid chromatography/tandem mass spectrometry (LC/MS/MS) has been developed and critically evaluated. The progesterone along with its internal standard (progesterone-13C2) was extracted from the serum matrix using liquid-liquid extraction prior to reversed-phase LC/MS/MS. The accuracy of the measurement was evaluated by a comparison of results of this method on a lyophilized human serum reference material for progesterone [Certified Reference Material (CRM) 347] with the certified values determined by gas chromatography/mass spectrometry (GC/MS) reference methods and by a recovery study for the added progesterone. The results of this method for progesterone agreed with the certified value within the uncertainty of the measurements for the CRM 347. The recovery of the added progesterone ranged from 100.1 to 100.9%. This method was applied to the determination of progesterone in frozen serum samples from three individual female donors with the progesterone concentrations ranging from 0.151 to 24.42 ng/g. Excellent reproducibility was obtained with within-set coefficients of variation (CVs) ranging from 0.1 to 1.4%, and between-set CVs ranging from 0.3 to 0.5%. Excellent linearity was also obtained with correlation coefficients of all linear regression lines (measured intensity ratios vs mass ratios) ranging from 0.9998 to 1.0000. The detection limit at a signal-to-noise ratio of approximately 3 was 1.8 pg of progesterone. This well-characterized LC/MS/MS method for serum progesterone, which demonstrates good accuracy and precision, low susceptibility to interferences, and comparability with GC/MS reference methods, qualifies as a reference measurement procedure that can be used to provide an accuracy base to which routine methods for progesterone can be compared and that will serve as a standard of higher order for measurement traceability.
Philip Roth’s Great Books: A Reading of The Human Stain
Philip Roth belongs to the first generation of American novelists for whom a university education in the liberal arts was the norm. This essay charts Roth’s developing acquaintance with classical literature, the starting point for Great Books courses in the 1950s, and the implications for his fiction of his understanding of the difference in scope and purpose between the two representative classical genres. It focuses on The Human Stain (2000), the novel in which he reflects most directly upon what tragedy and epic once did, and what might happen to novels if they became more like the one or the other.