Increasing the sensitivity of delta C-13 and delta N-15 abundance measurements by a high sensitivity elemental analyzer connected to an isotope ratio mass spectrometer

A common elemental analyzer system connected to a temperature-controlled gas chromatography (GC) column and coupled to an isotope ratio mass spectrometer was improved to decrease the determination limit for a simultaneous stable isotope ratio measurement of nitrogen and carbon dioxide. The additional use of a special ashtray system to collect the combustion residuals permitted more time-efficient work. These modifications to the elemental analyzer allowed precise measurements to be made down to 1.5 mu g nitrogen and 10 mu g carbon for stable isotope analysis. Low system background values and an acceptable signal-to-noise ratio have made an additional blank correction for these low sample measurements unnecessary. We provide a precision of this stable isotope analysis for lowest amounts of 1.2-2 mu g nitrogen with a standard deviation of +/- 0.496 parts per thousand (n=27) and for 8.2-15 mu g carbon with a standard deviation of +/- 0.257 parts per thousand (n=31) across different sample runs under stipulated conditions. This application can be established in an automatic mode without cryofocusing procedures. Copyright (c) 2007 John Wiley & Sons, Ltd.