Gas chromatography-mass spectrometry

In most cases, organic substances are multicomponent mixtures of individual components. For example, 400 components (i.e., 400 individual organic compounds) have been shown to have fried chicken odor. The analyst's task is to determine how many components make up an organic substance, find out what these components are (identify them) and find out how much of each compound is contained in the mixture. A combination of chromatography and mass spectrometry is ideal for this. Gas chromatography is best suited for combination with the ion source of an electron impact or chemical ionization mass spectrometer, since the compounds are already in the gas phase in the column of the chromatograph. Instruments in which a mass spectrometric detector is combined with a gas chromatograph are called gas chromatography mass spectrometers (GC / MS).

Chromato-Mass Spectrometry with Agilent 6890 GC 5973N GC / MSD 7683 Autosampler

The mass spectrometer has long been regarded as an excellent detector for gas chromatography. Both the gas chromatograph and the mass spectrometer are, in principle, relatively simple instruments, and the analytical data obtained with each of them are easy to understand and use. When these two instruments are directly connected into a single gas chromatography / mass spectrometric system, the capabilities of such a system are not simply the sum of the capabilities of each instrument; analytical capabilities are increasing exponentially. The spectra obtained with the help of a mass spectrometric detector provide such information about the qualitative composition of the sample, which cannot be provided by other gas chromatographic detectors. The mass spectrometric detector is more sensitive, in addition, it degrades the sample, provides information on mass, and distinguishes between homologues rather than isomers.

The first step in gas chromatography-mass spectrometric analysis is usually scanning over the entire mass range. Identification is carried out using a library of spectra, most often stored in the computer memory, which simultaneously controls the operation of the detector. The study of characteristic peaks and molecular ions plays an important role in the identification of a compound.

The next step is a qualitative analysis, for which the method of registration of individual ions (SIM) is used. For this, a filter is used to examine only a few types of ions and thereby increase the sensitivity.

Finally, all individual ion waveforms are summed and plotted on a single time base to obtain an All Ion in Sample (TIC) chromatogram.

Nowadays, mass spectrometers are produced only in a set with a computer. The bank of mass spectral data, which the customer receives together with the device, provides great assistance in identification. As the mass spectrometric analyzes are performed, new results are continuously entered into the computer memory, replenishing the data bank. If it is necessary to use the bank, the analyst sends a request to the computer, and the computer itself finds in the memory the spectrum that better than others corresponds to the spectrum being recorded at the moment. Both spectra appear on the screen, and now it only remains to compare the two spectral patterns. Comparison of spectra, that is, a kind of recognition by fingerprints, is much easier for identifying unknown substances than the reconstruction of molecules from separate fragments. The only necessary condition for such identification is the presence in the database of the spectrum of the very substance that was received for analysis.

Gas chromatography-mass spectrometry applications

Chromato-mass spectrometry has found wide application in various fields of chemistry, medicine, pharmaceutical production, environmental monitoring and technological control in industry.

Development of new drugs to save people from previously incurable diseases and control of drug production, genetic engineering and biochemistry, proteomics. Control over the illegal distribution of narcotic and psychotropic drugs, forensic and clinical analysis of toxic drugs, analysis of explosives is unthinkable without mass spectrometry.

Finding out the source of origin is very important for solving a number of issues: for example, determining the origin of explosives helps to find terrorists, drugs - to fight their spread and block the paths of their traffic. The economic security of the country is more reliable if the customs services can not only confirm by analyzes in doubtful cases the country of origin of the goods, but also its compliance with the declared type and quality. And the analysis of oil and oil products is needed not only to optimize oil refining processes or geologists to search for new oil fields, but also to identify those responsible for oil spills in the ocean or on land.

In the era of “chemicalization of agriculture”, the question of the presence of trace amounts of chemicals used (for example, pesticides) in food products has become very important. In scanty quantities, these substances can cause irreparable harm to human health.

A number of technogenic (that is, not existing in nature, but appearing as a result of human industrial activity) substances are supertoxicants (having a poisonous, carcinogenic or harmful effect on human health in extremely low concentrations). An example is the well-known dioxin.

The existence of nuclear power is unthinkable without mass spectrometry. With its help, the degree of enrichment of fissile materials and their purity are determined.

Of course, medicine is not complete without mass spectrometry. Isotope mass spectrometry of carbon atoms is used for direct medical diagnosis of human infection with Helicobacter pylori and is the most reliable of all diagnostic methods. Also, mass spectrometry is used to determine the presence of doping in the blood of athletes.

It is difficult to imagine an area of human activity where there would be no place for mass spectrometry. Let's just list: analytical chemistry, biochemistry, clinical chemistry, general chemistry and organic chemistry, pharmaceuticals, cosmetics, perfumery, food industry, chemical synthesis, petrochemistry and oil refining, environmental control, production of polymers and plastics, medicine and toxicology, forensics, doping control, control of drugs, control of alcoholic beverages, geochemistry, geology, hydrology, petrography, mineralogy, geochronology, archeology, nuclear industry and energy, semiconductor industry, metallurgy.