Determination of nitrogen-15 isotope fractionation in tropine: evaluation of extraction protocols for isotope ratio measurement by isotope ratio mass spectrometry

Rapid Communications in Mass Spectrometry : RCM
Roland MoliniéRichard J Robins

Abstract

N-Demethylation of tropine is an important step in the degradation of this compound and related metabolites. With the purpose of understanding the reaction mechanism(s) involved, it is desirable to measure the 15N kinetic isotope effects (KIEs), which can be accessed through the 15N isotope shift (Deltadelta15N) during the reaction. To measure the isotope fractionation in 15N during tropine degradation necessitates the extraction of the residual substrate from dilute aqueous solution without introducing artefactual isotope fractionation. Three protocols have been compared for the extraction and measurement of the 15N/14N ratio of tropine from aqueous medium, involving liquid-liquid phase partitioning or silica-C18 solid-phase extraction. Quantification was by gas chromatography (GC) on the recovered organic phase and delta15N values were obtained by isotope ratio measurement mass spectrometry (irm-MS). Although all the protocols used can provide satisfactory data and both irm-EA-MS and irm-GC-MS can be used to obtain the delta15N values, the most convenient method is liquid-liquid extraction from a reduced aqueous volume combined with irm-GC-MS. The protocols are applied to the measurement of 15N isotope shifts during growth of...Continue Reading

References

Jan 15, 1999·Journal of Magnetic Resonance·H BarjatR Freeman
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Sep 27, 2003·Analytical and Bioanalytical Chemistry·Torsten C SchmidtKlaus Steinbach
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Jul 1, 2005·Rapid Communications in Mass Spectrometry : RCM·Roland MoliniéRichard J Robins
Aug 8, 2006·Magnetic Resonance in Medicine : Official Journal of the Society of Magnetic Resonance in Medicine·Bryan KresslerYi Wang
Nov 23, 2006·Journal of Pharmaceutical and Biomedical Analysis·Patrick GiraudeauSerge Akoka
Jul 1, 1997·Isotopes in Environmental and Health Studies·P F Cook

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