Troubleshooting your Micro-Ion Vacuum Gauge

Last month when I wrote "When GC Injection Issues Aren't Syringe Issues", I promised an explanation on why the vacuum gauge no longer works on my 5975C.

This past year, we have been experimenting a lot with Concurrent Solvent Recondensation - Large Volume Splitless Injection (CSR-LVSI). Unlike most large volume injection techniques, CSR-LVSI does not vent excess solvent before transferring analytes to the analytical column. Therefore, the amount of solvent delivered to the MSD is easily 10x the normal amount (assuming 10 µL CSR-LVSI injections vs. 1 µL standard injections).

Low pressure measuring devices are generally hot-filament ionization gauges. The hot-filament in the ion gauge can "burn out," just like the filaments on the ion source, so if you are going to be experimenting with large volume injection, we recommend that you disable your ion gauge via the Vacuum menu under the Tune and Vacuum Control screen in Chemstation.

What are the symptoms of a malfunctioning vacuum gauge? An incorrect reading, and a red indicating LED on the back of the ion gauge (green means working properly, and yellow indicates that the gauge is not active).