A new gas inlet system for an isotope ratio mass spectrometer improves reproducibility

We have developed a new inlet system for a gas sample isotope ratio mass sp ectrometer (IRMS). It is based on the well-known open split design from the gas chromatography/mass spectrometry (GC/MS) system due to its simplicity. The advantages over the conventional double inlet system with the metal be llows design Include an improved reproducibility mainly due to a highly con trollable pressure and temperature adjustment, a markedly lowered memory ef fect due to an uninterrupted gas flow through the ion source which limits a dsorption/desorption processes on surfaces, and a single inlet capillary ci rcumventing problems of asymmetrical behavior of sample and reference inlet paths, Furthermore, sample consumption is of the same order as for convent ional measurements (i,e, about 0.4 mmol per hour), of which however only 2 mu mol/h is used for the actual isotope ratio determination since the major gas amount acts as a gas flow seal against the atmosphere, corresponding t o a 100-200 fold overkill. This may be improved in future systems. Copyrigh t (C) 2000 John Wiley & Sons, Ltd.