Drug Identification with Gas Chromatography Mass Spectrometry
Uploaded by Admin on Jan 22, 1999
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...