Highly sensitive and selective analysis of urinary steroids by comprehensive two-dimensional gas chromatography combined with positive chemical ionization quadrupole mass spectrometry

Comprehensive two dimensional gas chromatography (GC x GC) provides greater separation space than conventional GC. Because of fast peak elution, a time of flight mass spectrometer (TOFMS) is the usual structure-specific detector of choice. The quantitative capabilities of a novel GC x GC fast quadrupole MS were investigated with electron ionization (EI), and CH4 or NH3 positive chemical ionization (PCI) for analysis of endogenous urinary steroids targeted in anti-doping tests. Average precisions for steroid quantitative analysis from replicate urine extractions were 6% (RSD) for EI and 8% for PCI-NH3. The average limits of detection (LODs) calculated by quantification ions for 12 target steroids spiked into steroid-free urine matrix (SFUM) were 2.6 ng mL(-1) for EI, 1.3 ng mL(-1) for PCI-CH4, and 0.3 ng mL(-1) for PCI-NH3, all in mass scanning mode. The measured limits of quantification (LOQs) with full mass scan GC x GC-qMS were comparable with the LOQ values measured by one-dimensional GC-MS in selected ion monitoring (SIM) mode. PCI-NH3 yields fewer fragments and greater (pseudo) molecular ion abundances than EI or PCI-CH4. These data show that a benchtop GC x GC-qMS system has the sensitivity, specificity, and resolution to analyze urinary steroids at normal urine concentrations, and that PCI-NH3, not currently available on most GC x GC-TOFMS instruments, is of particular value for generation of structure-specific ions.