GC-MS
Gas chromatography-mass spectrometry (GC-MS) is a method from chemical analytics with the aid of which organic compounds can be identified and quantified.
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This is how Quality Analysis supports you with GC-MS
In our accredited test laboratory, we separate complex organic mixtures with the aid of our modern gas chromatograph (GC) coupled to a mass spectrometer (MS) to offer you a reliable, qualitative and quantitative analysis of your sample, which we provide in a detailed test report. Our experts are also available at short notice.
How does GC-MS work?
During GC-MS, a gas chromatograph is coupled to a mass spectrometer via a heated transfer connection. The gas chromatograph is used to separate the sample analysed; the substance to be analysed is identified in the mass spectrometer.
The role of the gas chromatograph in GC-MS
The gas chromatograph is used to separate an organic mixture. For this purpose, the vaporised substance is injected into the separation column in the chromatograph. An inert gas, the mobile phase, flows through the column as the stationary phase. Due to their physical-chemical characteristics, each component in the mixture has a different, characteristic mobility.
Today the separation column, in most cases, no longer consists of a long, thin glass tube, instead it is a capillary mesh with a total length of up to 100 metres. Capillary separation columns are particularly suitable for the separation of highly complex mixtures.
In the gas chromatograph, it is also possible to separate reliably very complex mixtures, however only as far as they can be vaporised without decomposition and their molecular mass is low (normally less than 1,000 daltons). Certain substances, so-called critical pairs, cannot be separated.
Ionisation – prerequisite for the analysis
The substances separated must be ionised so that mass separation is possible. This ionisation is mostly undertaken using electron impact ionisation (EI), that is using ionising radiation; however other methods are also used. After the ionisation, the original molecules are available as single charged ions. EI is not only of very universal application, it also makes it possible to draw conclusions about the molecular and structural formula of the substances based on the characteristic molecular fragments.
Mass separation and detection: the production of spectra
Mass separation is undertaken by means of the application of electrical and/or magnetic fields that separate ions based on their mass-to-charge ratio. The mass spectra are also acquired using either electrical or magnetic fields, so-called ion traps, or using quadrupole analysers; time-of-flight analysers (TOF) are increasingly used in complex mass spectrometers.
Various methods are also established for the detection of the ions, these include special electron tubes such as photomultipliers or secondary electron multipliers (SEM); Faraday cups and scintillation detectors, specifically the Daly detector, are also used.
The challenges of GC-MS and their solutions
For a long time with all detection methods, the user faced the challenge that the acquisition of the spectra could be slower than the separation in the gas chromatograph. The consequence was a reduction in the detection sensitivity or the quality of the spectra. Modern units, however, are able to acquire several complete mass spectra per second. The detection limits during the analysis of selected ions are in the meantime 10-14 mol.
The practical use of GC-MS
Its universal application makes gas chromatography-mass spectrometry a widely used analytical method for analytical chemistry. It can be used for the analysis of all organic compounds, provided these compounds can be vaporised. In the following it is therefore only possible to give a small insight into the varied applications of this analytical method.
Pharmaceutics and pharmacology
In PHARMACEUTICS AND PHARMACOLOGY, GC-MS is used both for the analysis of chemical substances in the laboratory as well as for in vivo research. It is used, for example, during the determination of the mass and analysis of the structure of substances in medicine production, and also for the verification of medicine-related metabolites in samples from the human body.
Food chemistry
In the food industry, GC-MS is used for the quantitative and qualitative assessment of the constituents as well as for the identification of foreign substances. Closely linked to these aspects are toxicological tasks during which GC-MS makes an important contribution to food safety.
In summary: GC-MS
Gas chromatography-mass spectrometry (GC-MS) is used for chemical analytics because, with its assistance, it is possible to analyse all substances that can be vaporised. The gas chromatograph is used to separate the sample; the quantitative and qualitative assessment takes place in the mass spectrometer. The method is used, for example, in pharmaceutics, food chemistry and numerous other areas.
