GC-MS Chromatography or Gas chromatography-mass spectrometry is one type advance analytical technique that is used to separate, identify and quantify volatile components in a sample to ensure the quality of products in the chemical industry; or to measure toxic substances in soil, air, or water. This technique relates to mixing a small amount of the sample with the mobile phase and passing it through a column filled with the stationary phase.
This versatile technique is the combination of two powerful techniques; gas chromatography and mass spectrometry. The low molecular weight compounds can be analyzed easily by this Gas chromatography-mass spectrometry technique. It is possible to analyze many relatively low molecular weight compounds in this process. The solid, gaseous, and liquid samples are used in GC-MS analysis to separate, identify and quantify volatile and semi-volatile compounds.
In GC, the constituent of various components of a sample mixture are separated as well as how much of each component is present. GC detector is generally two-dimensional and includes the retention time on an analytical column and the detector response. The chemical structures, elemental constituents of molecules, and molecular weight can be analyzed by using Mass spectrometry which measures the mass-to-charge ratio (m/z) of charged particles.
GC-MS produces 3D data, including chromatograms for qualitative and quantitative analysis as well as mass spectra for confirming the identity or identifying various chemical compounds.
GC-MS Chromatography Principle
The GC-MS Chromatography instrument is used to separate the chemical mixture (the GC component) and quantify the components at a molecular level (the MS component). The working principle of this tool is that a mixture will separate into individual substances when heated strongly. The sample which is to be tested is injected into the inlet of GC.
The sample will vaporize and sweep into a chromatographic column by a carrier gas such as helium. The sample will flow the column and the components in the mixture of interest will be separated by virtue of their relative attraction with the coating of the column (stationary phase) and the carrier gas (mobile phase). The remaining part of the column will pass through a heated transfer line and ends at the entrance to the ion source where components eluting from the column are converted to ions. A beam of electrons hits the sample molecules then molecular ion formation will occur and produce a ‘fingerprint’ to identify the molecular structure.
GC Components
Carrier gas system: The carrier gas in Gas chromatography-mass spectrometry helps to transfer the sample into the main column for separation. The most used carrier gases in this system are helium, nitrogen, argon, and hydrogen.
Sample injection system: A micro syringe is used to inject the sample into a flash vaporizer port at the head of the column. The sample port temperature should be kept at about 50°C higher than the boiling point of the least volatile component of the sample mixture.
Oven: This part is used to heat the sample mixture and create a suitable thermal environment for the elution of chromatographic peaks.
GC-columns: There are two types of GC chromatography columns available namely packed columns and capillary columns. These columns are made of glass or stainless steel tubes and contain a stationary phase, typically a polymeric material.
Detector: This part is called the brain of the chromatographic system which helps to record the chromatogram based on certain characteristics and helps us identify the compounds easily. This part is situated near the column to avoid the detection of the sample before decomposition.
Interface: The GC-MS interface is a device that is used to transport the effluent from the gas chromatography column to the mass spectrometer. The temperature of this part should be set above the boiling point of the highest-boiling component of the sample.
MS components
The mass spectrometry in this tool comprises a sample input system, an ion source for splitting the sample, a mass analyzer, detectors, and a readout device.
Types of GC-MS Chromatography
There are three types of GC-MS Chromatography which are given below:
Single quadrupole GC-MS Chromatography: This instrument contains only one quadrupole mass spectrometry system for the targeted selected ion monitoring (SIM) or untargeted full scan acquisition analysis of the sample. This technique is very suitable for screening the pesticides in food and environmental samples, screening biological samples for illegal drugs, and screening water samples for various volatile organic chemicals.
Triple quadrupole GC-MS Chromatography: This instrument contains a triple quadrupole mass spectrometry system for the analysis of the highest possible level of sensitivity since it offers a better level of selectivity. A default setting known as selective reaction monitoring (SRM) mode should be set for this tool at the time of use. This monitoring helps to limit interference from background ions and provides a high signal-to-noise ratio.
HRAM GC-MS Chromatography: It is the most modern version and consists of a high-resolution accurate mass (HRAM) mass spectrometer to evaluate a comprehensive characterization of samples with high confidence. Actually, it is the combination of a triple quadrupole GC-MS/MS with full-scan facilities. It is suitable for precise targeted analysis and reliable identification of unknown compounds.
Advantages of GC-MS Chromatography
The sample can be identified by this technique very easily with a good confidence level. The analysis needs less time as well as thermally labile. It is highly sensitive and provides high-resolution results. A small amount of sample is required for this rapid analysis system. It is a cost-effective process for quantitative analysis.
Limitations of GC-MS chromatography
The main disadvantage of the Gas chromatography-mass spectrometry system relates to insufficient volatility of the species to be separated. A very high temperature creates low detection limits at high resolution.
Applications of GC-MS Chromatography
Oil and gas analysis: This technique is important to determine the energy content, CHA, SIMDIS, and H2S/organic sulfur content of natural gas and natural gas condensates.
Medicine: This versatile technique is used for screening tests to detect several congenital metabolic diseases. The trace level of harmful components can be identified in the urine of patients with genetic metabolic disorders.
Biological and pesticide detection: It is used to detect dibenzofurans, dioxins, herbicides, sulfur, pesticides, phenols, and chlorophenols in air, soil, and water in our environmental constituents.
Pharmaceutical Applications: It is used in the pharmaceutical industry for conducting research and development, production, and quality control. It is possible to identify the impurities in active pharmaceutical ingredients by this technique.
Food and Fragrance Analysis: This process is very suitable for analyzing the fatty acids, esters, aldehydes, alcohols, and terpenes present in food and beverages. GC-MS system is used very much for controlling the quality of various oils such as lavender oil, olive oil, spearmint oil, essential oils, perfumes, fragrances, allergens, menthol, and syrups.
Academic research: This technique allows for evaluating the characterization and identification of newly synthesized or derivatized compounds.
Industries: The GC-MS Chromatography analytical technique is used for analysis in food, environmental, forensics, anti-doping, and consumer products.
References
1.Karasek, F. W., & Clement, R. E. (2012). Basic gas chromatography-mass spectrometry: principles and techniques. Elsevier.
2.Hites, R. A. (1997). Gas chromatography mass spectrometry. Handbook of instrumental techniques for analytical chemistry, 1, 609-625.
