GC-Mass Spec.

GC-MS (Gas Chromatography Mass Sepectrometery)
Carrier: gas, usually N2 or He
Stationary phase: Silicon related compound
Detector: Mass Spectrometer (MS)

In the MS’ ionising chamber, compounds are being bombarded with electron, causing the compound to ionise into captions, and formation of radicals. Such radicals and compound are unstable. It will eventually break up into fragments.

At the quadripole, different electromagnetic field is applied at specific time. Compounds of the right electrical charge will pass through the quadripole.

Positively charged compound will be attracted to the High Energy Dynode (HED), which will later discharged electron. Electrons pass through the electron multiplier, which will produce more electrons when electrons hit the multiplier. This amplifies the compound’s signal. The electron will eventually be converted to electrical signal, producing a spectrum.

The spectrum is compared with a reference spectrum for identification. GC-MS may be used for further identification from other chromatographic methods. It is used as an initial screening for exceeding amount of pesticide. For further quantification and detection of minor amounts of pesticide, compound specific GC detector are used.