Neurosteroid analysis by gas chromatography–atmospheric pressure photoionization–tandem mass spectrometry

• GC is interfaced with APPI–MS/MS using simple, commercially available hardware.
• With chlorobenzene as dopant, trimethylsilylated steroids form abundant radical cations with minimal fragmentation in GC–APPI–MS.
• The method shows good sensitivity and quantitative performance.
• The product ion spectra of the TMS-derivatized steroids are similar to EI spectra.

A new and simple APPI interface employing commercially available hardware is used to combine GC to MS. The feasibility of the method is demonstrated in the analysis of urine samples for neurosteroids as their trimethylsilyl (TMS) derivatives. The effect of different dopants (chlorobenzene, toluene, anisole) on the ionization of the TMS derivatives was investigated. With chlorobenzene, the TMS derivatives produced intense molecular ions with minimal fragmentation, and chlorobenzene was selected as best dopant. Protonated molecules in addition to intense molecular ions were produced with toluene and anisole. The performance of the method was verified in the analysis of human urine samples. Chromatographic performance was good with peak half-widths of 3.6–4.3 s, linearity (r2 > 0.990) was acceptable, limits of detection (LODs) were in the range of 0.01–10 ng mL−1, and repeatability was good with relative standard deviations (rsd%) below 22%. The results show that the method is well suited for the determination of neurosteroids in biological samples.

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