Determination of the natural abundance δ15N of nortropane alkaloids by gas chromatography–isotope ratio mass spectrometry of their ethylcarbamate esters Katarzyna Kosieradzka, Illa Tea, Emmanuel Gentil and Richard J. Robins Elucidation of Biosynthesis by Isotopic Spectrometry Group, Unit for Interdisciplinary Chemistry: Synthesis-Analysis-Modelling (CEISAM), University of Nantes—CNRS UMR6230, 2, rue de la Houssinière, 44322 Nantes, France Analytical Bioanalytical Chemistry (2010), V396, pp1405–1414, doi: 10.1007/s00216-009-3354-z A method is described which allows both the quantification of nortropane alkaloids and the determination of their natural abundance δ15N values. The protocol exploits the derivatisation of the alkaloids by reaction with ethyl chloroformate in aqueous medium and the quantitative extraction of the ensuing ethylcarbamate esters. The improved chromatographic properties of these derivatives gives ample separation of the isomeric nortropine and norpseudotropine for measurement of their δ15N (‰) values by isotope ratio mass spectrometry interfaced to gas chromatography. Adequate separation could not be achieved with the underivatised compounds. Repeatability and precision are sufficient to allow differences in the δ15N values (Δδ15N)>0.8‰ to be measured, with a standard deviation routinely ∼0.3‰. The methodology has been tested by determining the changes in the δ15N values of nortropine and norpseudotropine during degradation by cell suspension cultures of a Pseudomonas strain expressing a specific capacity for tropine catabolism. The precision and reproducibility are shown sufficient to allow the evolution of the δ15N values to be followed during the fermentation.