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Drug Identification With Gas Chromatography Mass Spectrometry

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Drugs are used everyday by people in many different ways for many different reasons. Drug testing has become a standard in pre-employment testing, because of the wide variety of drug use in today's society. Drugs tested for by a possible employer include Cocaine (crack), Amphetamines (crystal), Opiates (codeine, morphine, heroin), PCP (phencyclidine), and Marijuana. Gas chromatography/mass spectrometry is used to test hair and urine samples of possible drug abusers or job applicants, and it is the best method for the testing of drug use. Gas chromatography and mass spectrometry are two different methods for identifying chemical substances, and the two instruments have be coupled together to perform a highly complementary analytical function. The gas chromatograph and the mass spectrometer have theories behind how their techniques work, and specific forensic applications for their instrumentation.

The history and theory of the gas chromatography started over forty years ago with the invention of the capillary column. The gas chromatograph offers rapid and very high-resolution separations of a very wide range of compounds, with the only restriction that the analyzed substance needs to have sufficient volatility. The theory behind the mass spectrometer is to use the difference in mass-to-charge ratio (m/e) of ionized atoms or molecules to separate them from each other. Mass spectrometry is therefore useful for quantitation of atoms or molecules and also for determining chemical and structural information about molecules. Molecules have distinctive fragmentation patterns that provide structural information to identify structural components.

The combination of the gas chromatograph and mass spectrometer is very easy, because both instrument needs to be modified in excess and both are analyzed in the gas phase and have comparable sample levels and temperature ranges. The ! most important feature of the tw o instruments being coupled is that they perform complementary analytical functions.The instrumentation of the gas chromatograph/mass spectrometer is very complex. The instrument's parts include an injector, a carrier gas, a column, a separator, an ionization source, mass separator, and an ion detector.

The injector is located on the gas chromatograph and is where the sample gas is injected into the instrument to start the process. The sample gas is then mixed with a carrier gas, which is the mobile phase in gas chromatography. The mixture proceeds into the capillary column where the separation of the sample begins. The capillary column is 15 to 60 meters in length and .25 to .75 millimeters in diameter. Once through the capillary column the now separated sample enters the separator. The separator connects the gas chromatograph with the mass spectrometer, and separates the carrier gas from the separated components of the mixture.

The sample now enters the mass spectrometer's ionization source where the sample molecules are fragmented and created into! positively charged ions by high beam electrons. The fragmented positively charged ions now pass through the mass separator, which is a magnetic field. The mass separator isolates the fragmented sample into their masses. The isolated masses are read by an ion detector and then displayed as a mass chromatogram.

A mass chromatograph is a graph of ion m/e abundance in relation to time. The gas chromatograph/mass spectrometer or GC/MS produces a mass chromatogram of a substance that acts like a fingerprint for a chemical substance. The idea that a GC/MS produces a fingerprint for a chemical substance makes this instrument a very attractive option when testing for drug identification, and testing people for drug use. Forensic scientists find a drug's identification by using a GC/MS, and use the mass chromatogram in comparison with the test results of another unknown mass chromatogram. If the two mass chromatograms match then the tested chemical substance is that drug it was matched against. Another application is using a GC/MS and testing hair or urine samples of people to determine if the subject uses drugs.

Drugs tested for might encompass such well-known drugs as Cocaine (crack), Amphetamines (crystal), Opiates (codeine, morphine, heroin), PCP (phencyclidine), and Marijuana. Today, gas chromatography/mass spectrometry has become the premier technique for separations and analysis of drugs. Employers will often test prospective employees for drug use. They test with either hair or urine samples of the prospective employee, and run the sample(s) through a GC/MS to determine if the possible employee has used drugs. They determine this by comparing mass chromatograms of known drugs with that of the test sample. The gas chromatograph/mass spectrometer is known as the best resource to prove the identification of a chemical substance, such as a drug, because of the mass chromatographs that act like a fingerprint of a chemical substance.

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"Drug Identification With Gas Chromatography Mass Spectrometry." 123HelpMe.com. 18 Apr 2014
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