High Precision sigma exp(13)C Analysis Of Steroids By Comprehensive Two Dimensional Gas Chromatography Combustion Isotope Ratio Mass Spectrometry

Abstract

Carbon Isotope Ratio analysis of urinary steroids using GCC-IRMS is a recognized test to detect illicit doping with synthetic testosterone. However, there are currently no universally used steroid isotopic standards (SIS) for calibration of GCC-IRMS data between antidoping labs. One dimensional GC (1DGC) has This thesis focuses on limitations with the separation of closely eluting components. challenges which have limited the scope of antidoping tests with existing instrumentation. Two steroid mixtures were prepared, one with four derivatized steroids and one with three underivatized steroids. Steroids were calibrated using a Thermo Finnigan 253 IRMS and calibrated against NIST RM 8559, traceable to the international standard VPDB. Absolute sigma exp(13)C sub(VPDB) and delta sigma exp(13)C sub(VPDB) values from randomly selected SIS ampoules indicate uniformity of steroid isotopic composition within measurement reproducibility, SD (sigma exp(13)C) less than 0.2 0/00. Recently, two dimensional GC (GC x GC) has developed into a commercial technique and has been applied to natural mixtures because it has ten times the peak capacity and sensitivity compared to 1D GC. Here the very first coupling of fast GC to IRMS with peak widths one-fifth of any previously reported GCC-IRMS system is shown. Fast GC was accomplished by systematically removing sources of peak broadening. The first coupling of comprehensive GC x GC to on-line combustion IRMS was accomplished by interfacing to an optimized low dead volume combustion interface to preserve less than 300 ms wide GC2 peaks, modifying the IRMS detector to enable fast detection, and advancing software to handle isotopic time shifts of less than one bin (40 ms), and to integrate peak slices to recover isotope ratios. To avoid the addition of external carbons, analysis of underivatized steroids is preferred for IRMS analysis. Several column sets were evaluated for best dispersion A thick film polar GC1 column and a nonpolar GC2 of steroids in 2D analysis space. column were used for the detection of underivatized exogenous steroids and other drugs in a complex urine matrix using GC x GC-TOF-MS. The use of GC x GCTOF-MS allows for full mass spectrum scanning, enabling the detection and identification of unknowns or designer drugs in the urine matrix.