This section provides overview, applications, and principles of chromatographic gas. Also, please take a look at the list of 10 chromatographic gas manufacturers and their company rankings.
A gas chromatograph is an instrument used for qualitative and quantitative analysis of easily vaporizable compounds. It is commonly abbreviated as gas chromatography, and is sometimes written as GC, from the English abbreviation Gas Chromatograph. Along with high-performance liquid chromatography, it is a very well-known analytical technique.
Its principle is to vaporize a sample and then separate each component to determine the type and content of compounds. The greatest advantage of this method is that it can analyze volatile components even at very low concentrations. Currently, gas chromatographs are used in a wide range of fields, including pharmaceutical, food, and chemical industries, contributing to the foundation and development of science and technology.
Gas chromatograph and gas chromatography are similar terms, and the two are often confused, but the former (gas chromatograph) refers to "experimental equipment" and the latter (gas chromatography) refers to "separation operations using gas chromatography".
Gas chromatographs are used for separation and analysis of compounds in the fields of medicine, food, and chemistry. For example, it can be used to measure the concentration of hazardous substances and to analyze the components of gases generated in equipment. Note, however, that not all compounds can be analyzed. Due to its principle, gas chromatography generally cannot analyze non-volatile compounds with a boiling point of 400°C or higher, or unstable compounds that decompose at high temperatures. Inorganic metals, ions, and highly adsorbable compounds are also difficult to analyze for the same reason, and must be confirmed prior to analysis.
The principle of gas chromatography is very simple and consists of the following three steps:
First, the liquid sample is thermally vaporized. The vaporized components are transported to the column by a carrier gas. The vaporized components are adsorbed and distributed to the stationary phase (liquid phase) in the column, separated by component, and passed through the column. Since the speed at which compounds move through the column differs depending on the compound, the components with the fastest movement speed are first separated out of the column. Since each separated component is recorded as a peak by the detector, the type and concentration of the sample can be determined by comparing the retention time and peak area with those of the standard.
The main feature of this analytical method is that it can analyze volatile components that cannot be separated, identified, or quantitated by high-performance liquid chromatography.
The selection of the stationary phase to be used in the column of gas chromatography is very important. If a column with an appropriate stationary phase is not used according to the characteristics of the components, separation and analysis will be difficult.
Columns are broadly classified into two types based on the polarity of the stationary phase: nonpolar columns and highly polar columns.
A non-polar column is a column in which a compound with low polarity is used as the stationary phase. In such columns, low-polarity compounds are strongly retained in the low-polarity liquid phase as the stationary phase, resulting in slower migration rates and, thus, higher separation performance. Therefore, non-polar columns are suitable for the analysis of nonpolar compounds. In addition, nonpolar columns are more heat resistant than highly polar columns and can generally be used up to 350°C.
A highly polar column is a column in which a highly polar compound is used as the stationary phase. In such columns, highly polar compounds are strongly retained, which slows down their migration rate and results in high separation performance. As a result, these columns are suitable for the analysis of highly polar compounds. Also note that high polarity columns have low heat resistance, generally with an upper limit of around 250°C.
Due to their low volatility, highly polar organic low-molecular-weight compounds are generally difficult to separate and analyze using gas chromatography. However, depending on the structure of the target compound, it may be possible to derivatize it into a volatile compound using chemical methods, in which case separation using gas chromatography becomes possible. Therefore, such derivatization techniques are widely used for separating and analyzing compounds that are difficult to separate by high-performance liquid chromatography. One such example is the TMS derivatization of sugars and oligosaccharides, compounds with many hydroxyl groups, followed by GC analysis.
Detectors detect components separated by gas chromatograph columns and are used for different purposes.
Flame Ionization Detector (FID) detects ionized compounds by combustion of organic compounds in a hydrogen flame formed by air and hydrogen. Almost all organic compounds can be detected, and the sensitivity is extremely high.
Thermal Conductivity Detector (TCD) defects components by reading the temperature change of a filament based on the difference in thermal conductivity between the carrier gas and the target component. Both inorganic and organic components can be detected nondestructively.
Thermal Conductivity Detector (TCD) detects each component by amplifying the light of a specific wavelength generated from the element by combustion using a photomultiplier tube and converting the intensity of the light into an electrical signal. Sulfur compounds, phosphorous compounds, and organotin compounds can be detected.
Sulfur components are detected by measuring the light produced when chemical species (mainly SO) converted from sulfur compounds are excited by ozone and then return to their ground state using a photomultiplier tube.
This detector is suitable for the measurement of organic nitrogen compounds. When a compound containing phosphorus or nitrogen enters the rubidium salt in the hydrogen flame, it ionizes to form CN- and PO- ions, which are detected.
This detector is used for the selective detection of compounds with high neoelectronicity, such as organohalogen compounds, organometallic compounds, and nitro compounds. Components are detected by reading changes in voltage values to keep the ion current collected in the collector constant.
A gas chromatograph-mass spectrometer is an instrument that combines a gas chromatograph and a mass spectrometer via an interface. First, a sample containing multiple components is first separated into single components by the gas chromatograph, and then the mass spectrometer measures the MS spectra of the individual components to qualify the components and quantitate them from the spectral intensity of the ions.
Gas chromatograph-mass spectrometers are suitable for compositional analysis of various oils, qualitative analysis of organic solvents, qualitative and quantitative analysis of gases generated from various materials and pyrolysis-generated gas species, and VOC (volatile organic compounds) analysis in air, water, etc.
*Including some distributors, etc.
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