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Article Title

Evaluation of isotopic analogs as internal standard for quantitative determination of urinary 6-acetylmorphine by gas chromatography/mass spectrometry

Abstract

This study examined the accessibility of using 6-acetylmorphine-d3 (6- AM-d3) as the internal standard and trifluoroacetic anhydride, pentafluoropropionic anhydride, and hexamethyl-disilazane as the derivatizing agents in the quantitative analysis of 6-acetylmorphine (6-AM) by full scan mode and selective ion monitoring (SIM) mode gas chromatography / mass spectrometry (GC/MS). In this study, fragments with minimal interference between the analyte and the internal standard were evaluated and selected for quantitative determination. Calibration curves and precision analyses were further performed using these selection ions. In the full scan mode, there was a certain interference between the mass spectra of trimethylsilyl derivative of 6-AM and those of 6-AM-d3 at some fragment ions. This requires that there be careful selection of fragment ions for quantitative determination due to the potential cross-contribution and subsequent inaccurate results. On the other hand, 6-AM-d3 might be suitable as the internal standard in quantitative analysis of the trifluoroacetyl or pentafluoropropionyl derivative by GC/MS since the interference between the mass spectra of these derivatives of 6-AM and those of 6-AM-d3, was minimal. In the SIM mode, results were similar with those of the full scan mode. The suitable fragments were thus selected for the calibration curve and precision analysis by SIM GC/MS. Excellent linearity was obtained over the concentration range of 50-1000 ng/ml of 6-AM for their TFA, PFP, and TMS derivatives. Good precision was also obtained from within-run and between- run CVs for 6-TFA-AM, 6-PFP-AM and 6-TMS-AM at a concentration of 200 ng/ml. 6-AM-d3 was demonstrated to be a suitable standard in quantitative analysis of TFA-, PFP-, or TMS- derived urinary 6-AM in SIM node GC/MS analysis.

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