Comparison of a jet separator and an open splitter as an interface betweena multi-capillary gas chromatographic column and a time-of-flight mass spectrometer

A gas chromatographic/time-of-flight mass spectrometric (GC/TOFMS) interfac e is being developed for fast on-line analysis utilizing multi-capillary co lumn technology. A variable gap-distance jet separator has been constructed and its performance compared with that of a commercially supplied post-col umn open splitter recommended for use between the multi-capillary column an d a mass spectrometer. Both interfaces were found to be compatible with the GC/TOFMS system at high carrier gas flow-rates, facilitating high-speed an d high-resolution separations. The systems were investigated and tested wit h a mixture of volatile organic compounds (VOCs) with molecular masses from 85 to 166: dichloromethane, toluene, m-dichlorobenzene, o-dichlorobenzene and tetrachloroethylene. The optimum tip-to-tip gap distance corresponding to the highest efficiency of the jet separator was found to be 0.030 mm for each compound at carrier gas how-rates of 20, 40 and 60 ml min(-1) giving, in the ion source housing, ion gauge pressure readings of 1.6 x 10(-6), 5. 0 x 10(-6) and 5.8 x 10(-6) mbar, respectively. The efficiency of the jet s eparator (10-30% yields) was significantly higher than that of the open spl itter (6-9% yields). The observation that the open splitter did not provide a constant how-rate to the ion source was not in agreement with the manufa cturer's specifications. A method for measuring the gas flow-rates in all p arts of the equipment is described. The correlation between yield in the je t separator and molecular mass for the heterogeneous set of compounds studi ed was found to be less linear than usually reported for homologous series of compounds in jet separator studies. The result suggests that the pressur e conditions in the jet may be sufficient for the separation process to be partly controlled by diffusion rather than predominately by effusion. Copyr ight (C) 2000 John Wiley & Sons, Ltd.