Static Calibration_GC/MS

[christiana]

We own a a HP 5890 GC and a MS Trio.

Could I have information about static calibration? Searching in the internet and in the manual of MASPEC software doesn't help.

Thanks.

Christiana

[ods-at-pacific]

In GC/MS the term static calibration may refer to the calibration of the m/z scale with a constant partial pressure of the calibration compound during the process as opposed to introducing the calibration compound as a chromatographic peak. The static calibration could involve a constant flow of PFTBA gas into the ion source. The resulting voltages are then synchronized with known m/z values of the various ions to produce the calibration of the m/z scale.

[carras]

I was explained static calibration for a GC/MS way back ago. It is supposed to optimize the transmission of the ions along the quadrupole to increase sensitivity in SIM mode. It works like this: suppose you ion of interest is 351, you inject your standard using the following ions in acquisition: 358.6, 358.8, 351, 351.2 and 351.4 (the range can be larger). Then you look at your extracted ion chromatograms and identify the one with higher intensity in your peak. Let’s say it is 351.2, even though the "true" mass (as seen in scan mode) of your ion is 351, you should use 351.2 in your SIM method. The same experiment should be performed for every ion, every analyte and every instrument.

I haven’t tried it and I cannot really say whether it really works or not. In all honesty I cannot see why it is worth the effort, if you need more sensitivity you just can increase the mass window (the “low resolution” option in Agilent instruments). In my experience you get higher sensitivity without any apparent loss of selectivity, at least for my analytes.