Determination of the natural abundance δ15N of taurine by gas chromatography-isotope ratio measurement mass spectrometry

The measurement of the nitrogen isotope ratio of taurine (2-aminoethanesulphonic acid) in biological samples has a large number of potential applications. Taurine is a small water-soluble molecule which is notoriously difficult to analyze due to its polarity and functionality. A method is described which allows the determination of the natural abundance delta N-15 values of taurine and structural analogues, such as 3-amino-1-propanesulphonic acid (APSA), by isotope ratio mass spectrometry interfaced to gas chromatography (GC-irm-MS). The one-step protocol exploits the simultaneous derivatization of both functionalities of these aminosulphonic acids by reaction with triethylortho-acetate (TEOA). Conditions have been established which ensure quantitative reaction thus avoiding any nitrogen isotope fractionation during derivatization and workup. The differences in the delta N-15 values of derivatized and non-derivatized taurine and APSA all fall within the working range of 0.4 parts per thousand (-0.02 to 0.39 parts per thousand). When applied to four sources of taurine with various delta N-15 values, the method achieved excellent reproducibility and accuracy. The optimized method enables the determination of the natural abundance delta N-15 values of taurine over the concentration range 1.5-7.84 mu mol.mL(-1) in samples of biological origin. Copyright (C) 2010 John Wiley & Sons, Ltd.