Helium Saver Mode With Nitrogen Make-Up Cooling Gas for GC-MS With Cold EI

Cold EI uses helium as the column carrier and cooling make-up gases at ~50 mL/min. In the rare case that helium supply could be temporarily interrupted, nitrogen or hydrogen can be used, but hydrogen leads to decomposition at the GC injector, and thus, nitrogen is preferred. However, nitrogen leads to longer analysis time and/or reduced separation. We describe the use of helium as the column carrier gas and nitrogen as the cooling make-up gas. In this "Helium Saver" mode, the helium consumption is as in standard EI and nitrogen can be used alone in stand-by mode for further helium saving.