How to check if the CAD gas is properly working in Analyst® software

For research use only. Not for use in diagnostic procedures.

Answer

The collision associated dissociation (CAD) gas is an inert gas that breaks parent compound ions into smaller fragments, making it an important component of multiple reaction monitoring (MRM) methods in Analyst® software. It is introduced by diffusing a small stream of nitrogen through a small orifice into Q2 of a mass spectrometer. On rare occasions, this orifice might become blocked or out of calibration.

Usually, the CAD gas is set at medium or to the value of 9, and this results in a vacuum gauge pressure of 1.8–2.7 x 10 e-5 torr. For SCIEX legacy instruments (e.g., API 3200, 4000 and 5000 systems), this value could be as high as 4.0 x 10 e-5 torr. When the CAD gas is off, the vacuum gauge pressure is about 0.5 x 10 e-5 torr.

If you suspect CAD gas is not properly set, check the history of the vacuum gauge pressure on your instrument by checking the values stored in the sample file information for a particular .wiff file. (Vacuum gauge pressures are under the Log Information from Devices at Start of acquisition section under Vacuum Gauge.) Its a good idea to monitor the vacuum gauge pressure and keep daily or weekly records of the pressure readout, so that the current value can be compared with past values when the method was performing more satisfactorily.

For more information on how to view the file information pane, select this link: https://sciex.com/support/knowledge-base-articles/how-to-see-file-information-pane-in-analyst_en_us

For information on how to view the current vacuum pressure in the Detailed Status screen, select this link:
https://sciex.com/support/knowledge-base-articles/what-is-vacuum-gauge-pressure_en_us