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A gas chromatograph mass spectrometer (GCMS) identifies and quantifies substances by separating them into components and analyzing them with a computer. It is used in drug investigations, environmental sensing, and medical diagnosis. The process involves a gas chromatography step and a mass spectrometry step, which can be completed individually or simultaneously. The GCMS is used by law enforcement agencies, environmental agencies, and healthcare professionals.
A gas chromatograph mass spectrometer (GCMS) combines gas chromatography and mass spectrometry to identify and quantify substances. The process begins with the test substance being diluted with a gas or liquid and introduced into the machine. The GCMS separates the substance into components that need to be identified by a computer. Gas chromatograph mass spectrometers have a wide variety of uses, including illicit drug investigations, environmental sensing, and medical diagnosis.
The gas chromatography or GC step of the analysis typically involves placing a sample into the inlet port. The substance can be dissolved in an aqueous solution and injected into the chamber with a hypodermic needle. Once in the glass or stainless steel chamber, the compound travels to a furnace where it is transformed into a gas.
The gradual increase in temperature causes the compound to break down into its component parts, leave the chamber, and pass at varying rates into the detector. Electrically charged, the particles activate an electronic signal. The higher the concentration of particles, the stronger the signal created.
These signals are then analyzed by computer software. The computer produces a chromatogram with peaks indicating the retention times and signal strengths of the compounds. Knowing the retention times of various chemical compounds allows investigators to identify them.
Further analysis occurs in the mass spectrometer. Once compounds enter the spectrometer, they encounter an array of electrons or gases. Ionization occurs, breaking the compound into fragments, each having a specific atomic mass. These fragments are analyzed by compiling a fragment mass to charge ratio, or M/Z.
This information passes to the GC’s mass spectrometer computer which formulates a graph with peaks based on M/Z versus signal strength. Computer software typically includes a database of known M/Z ratios and signal strengths for different chemical molecules. The computer identifies the substances by comparing the acquired information with the library of known substances. The gas chromatograph mass spectrometer can complete each step of the analysis individually or simultaneously. Depending on the level of detail you want, the process can take 20 minutes or more than 20 hours to complete.
Law enforcement agencies use a gas chromatograph mass spectrometer when they suspect the presence of illegal drugs or poisonous substances. Environmental agencies use the technology to analyze air, soil or water samples for possible pollutants. Healthcare professionals use a GCMS on urine samples to detect chemicals found in individuals with certain metabolic disorders.
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