Both gas chromatography (GC) and mass spectrometry (MS) bring something to their union. GC can separate volatile and semivolatile compounds with great resolution, but it cannot identify them. MS can provide detailed structural information on most compounds such that they can be exactly identified, but it cannot readily separate them.
GC-MS can be used for the identification of unknown organic compounds both by matching spectra with reference spectra and by a priori spectral interpretation. The identification of reaction products by synthetic organic chemists is another routine application, as is the analysis of industrial products for control of their quality.
General Uses
1.Identification and quantitation of volatile and semivolatile organic compounds in complex mixtures
2.Determination of molecular weights and sometimes elemental compositions of unknown organic
compounds in complex mixtures
3.Structural determination of unknown organic compounds in complex mixtures both by matching
their spectra with reference spectra and by a priori spectral interpretation
为啥县gc后ms?
Briefly speaking, GC is mainly for separation while MSD is sort of a universal detector for qualitative and quantitative analysis.
The main principle of ms is like this: the sample is ionized into small molecule fragments by using EI or CI technique, then by detecting the relative abundances of various fragments we could get the structural information of certain compounds.
Usually, the sample injected into gc is the mixture of various compounds, but the sample for ms or msd should be pure substance, otherwise a bunch of components would be ionized all together and it will be difficult to obtain the molecule structural information for each components. So, only based on good separation effect can we get ideal analysis results.
GC-MSD analysis could be performed in either SCAN mode or SIM mode. In SIM mode, even if several target components were not well separated, we could still scan their specific ion(s) for quantitation. However, firstly SIM mode should be on the basis of accurate characterizations of all target components, secondly sometimes it might be difficult to determine the suitable specific ion(s) for those compounds with similar molecule structures. All in all, the ideal separation is the prerequisite for accurate analysis of the gc-msd system.