Topic: gas chromatography mass spectroscopy in forensic science

 

Gas chromatography – mass spectroscopy (GC-MS) is a quantitative analytical method which aims to separate mixture and identify the component in the mixture. This analytical method is commonly applied in forensic area in testing illegal drug abuse by analyzing tissue sample from the suspect. GC-MS is frequently used for hair analysis with high sensitivity in forensic drug abuse analysis. (Nakashima, Kenichiro) By applying GCMS, the suspected drug can be separated from the sample in gas chromatography and identify the drug using mass spectroscopy. Other than hair detection of drug abuse, GC-MS can detect drugs in blood, urine, oral and sweat tissue sample from the suspect. In drink driving, “the blood sample is analyzed for blood alcohol by gas chromatography.” (Clarke. 2008) This essay will demonstrate the theory of gas chromatography and mass spectroscopy, and different types of sample can be applied to conduct the analysis.

 

Gas chromatography is a type of chromatography which aims to separate mixture, in chromatography; there are two phases in chromatography namely mobile phase and stationary phase. Stationary phase is the phase that stays stationary during the analysis while mobile phase is the phase that moves along the stationary phase; the sample is dissolved in a solvent then injected in the system and moved along the stationary phase with the aid of mobile phase. When mobile phase move along stationary phase, compounds in sample interact with the stationary phase. There are different ways of interaction between the compounds and stationary phase; which depends on the polarity of compound and stationary phase. For example, when the stationary phase is polar, there are least interaction between the stationary phase and the polar compounds in the mixture, therefore; the most polar compound in the mixture will be the last compound to elute. There are different factors affecting the separation of mixture, “The degree of separation between the sample and the stationary phase is determined by flow rate, the nature of the stationary phase, the surface area exposed to the carrier gas, and the column temperature.” (Anonymous 2011) After the analysis of sample, a chromatogram is reported, the chromatogram shows the result of the analysis, a peak represent a component in the mixture; the area under the peak is proportional to the concentration of the compound. The gas chromatography consist of a inject port, column in oven, a detector and a recording integrator with a gas mobile phase. The sample was injected in the system, the oven heated up the sample and allowed the sample to vaporize, the sample was sent to the column and the mixture was separated, the detector detect the amount of components. This is a relatively efficient analysis among chromatography technique, the analysis time is short, however; this method is only available in analyzing volatile samples.

 

The mixture was separated in gas chromatography; however, the elution order in chromatography is estimated by the characteristic of the compounds, the identity of each peak is not examined in chromatography. Therefore, the sample was sent to the mass chromatography to confirm the identity of each compound.

 

Mass spectroscopy is a type of spectrometry that aim to identify compounds contain in the mixture after separation by chromatography. This is an analytical method that examining the identity of compound by indicating the mass of the molecule and fragments when molecules broke down. Mass spectrometry consists of a source, analyzer and a detector. The sample injected in the system, vaporized and ionized by heating up the sample in a high temperature in the ionization source, the molecule is also fragmented. The ions are accelerated by an electron beam and enter a strong electronic field, since the ions are charged, when the sample goes through the magnetic field, the sample moving in an arc. The radius is proportional to the mass to charge ratio, the mass of the molecule and fragments are differentiated. The detector detects the results from mass discriminator and generates the data to a spectrum in the recorder. There are several signals in the spectrum of a compound; this is the result of the fragmentation, the number of signals can be estimated as the number of carbon atoms which differently bonded. When the molecule loses a group, it produces another signal on the mass to charge ratio of the remained molecule. The height of signal is proportional to the relative abundance of the molecule.

When gas chromatography couple with mass spectroscopy, hydrogen gas is not suitable applying as the carrier gas since hydrogen can react with the compound molecule that affect the results in mass spectrometry by altering the mass to charge ratio.

 

Gas chromatography – mass spectroscopy is applied in forensic area for instance analyzing illegal drug abuse. Different types of samples can be collected for the illegal drug analysis, such as hair, blood, urine, oral and sweat tissue. In the sample of blood or urine, the drug are usually only detectable for a few hours or days, therefore, hair analysis is the preferred method to test the abuse of drugs since the drug residuals remain in hair for a longer time. Furthermore, analysis of hair by GC/MS/MS can also provide reliable data for use in administrative and judicial areas. (Rossi, Riccardo . 2005) Gas chromatography is only suitable analyzing volatile samples, however, many illegal drugs contain polar functional groups which result in involatile of compound, therefore; derivatization was applied to increase the volatility of compounds to let the sample suitable analyzing by GC. (Niessen. 2001) In hair sample analysis, GC-MS is applied to determine drug quantitatively and qualitatively; a sample having several types of drugs can be detected by this method. “GC-MS is applied to a qualitative analysis of three sample extracts from hair suspected of containing various drug compounds.” (Guthery. 2010) The hair sample is sent to the gas chromatography after sample preparation, different types of drugs can be separated in chromatography, and therefore, more than one drug can be detected. The separation of peaks is important in gas chromatography, changing the temperature can improve the resolution of the results, if more than one drug present in the sample, high resolution of the chromatogram become more important. Temperature programming, changing the temperature during the analysis, can be applied if necessary. To prepare the hair sample, obtain a hair segments and make up the sample solution with several reagents, the sample solution was sent to the GC-MS system and process the analysis. Other than the sample solution, several standard solutions, solution with known concentration prepared accurately, needed to be analyzed by GC-MS. (Rossi, Riccardo. 2005) After analyzing the sample solutions and the standard solutions, a curve can plot with the concentration verse the count; to determine the drug in the sample solution, read off the concentration from the curve with the count of the sample. Besides hair analysis, drug abuse analysis can also be analyzed in oral sample, “the main benefit of this body fluid is its noninvasive collection procedure compared with blood.” (Samyn, Nele. 2007) Although oral sample is a relatively convenient sample collecting method, the sample is easy to be contaminated. Saliva contains proteins, peptides, enzymes, glucose or even food residuals that may affect testing of drugs and analysis of concentration of drugs. In some cases, not enough available saliva samples can be collected; some techniques are applied to stimulate the production of saliva. However, “food and techniques designed to stimulate production of oral fluid can also affect the concentration of drugs.” (Drummer. 2006) There are possible errors in analysis of different types of samples, therefore; confirmatory test need to be conducted, gas chromatography mass spectrometry is applied in the analysis for confirm. (Huestis, 2006) Drug is often abused in sports, some athletes abuse stimulants and drugs to enhance strength. Therefore, chromatography with mass spectrometry is a common analytical method because of its sensitive, selective, and versatile nature. (Thevis, Mario. 2007) GC-MS can also separate a large number of substances in one analysis that increase the efficiency. In normal drug abuse, the hair sample is the preferred type of sample; however, in drug abuse in sports, urine is preferred because large quantities are available for analysis. (Pesce, Amadeo. 2011) When testing different type of stimulants, different type of sample preferred, for example; breath is preferred sample when testing alcohol. (Clarke. 2008) Collecting the suitable type of sample and avoid cross contamination is important for the drug analysis.

 

In conclusion, gas chromatography mass spectrometry is applied in forensic field for detection of illegal drug abuse and drug abuse in sports. The sample is collected and separated in gas chromatography, compounds contained in the sample is identified in mass chromatography. When GCMS is applied in analysis of illegal drug abuse, prepare sample solution and standard solution to plot a calibration curve and determine the concentration of drug in sample.  

 

 

 

 

 

Reference:

 

Anonymous (01/01/2011). "Gas Chromatography". LC GC North America (1527-5949), 29 (1), p. 12.

 

Clarke, Jickells, S. Negrusz. 2008. Clarke’s analytical forensic toxicology. Pharmaceutical press. London.

 

Drummer, Olaf H (01/08/2006). "Drug testing in oral fluid". Clinical biochemist reviews (0159-8090), 27 (3), p. 147.

 

Guthery, Bill (25/06/2010). "Qualitative drug analysis of hair extracts by comprehensive two-dimensional gas chromatography/time-of-flight mass spectrometry". Journal of chromatography. A (0021-9673), 1217 (26), p. 4402.

 

Huestis, Marilyn A (2006). "Modern analytical technologies for the detection of drug abuse and doping". Drug discovery today. Technologies (1740-6749), 3 (1), p. 49.

 

Nakashima, Kenichiro (01/06/2006). "Hair analysis: an excellent tool for confirmation of drug abuse". Analytical and bioanalytical chemistry (1618-2642), 385 (3), p. 413.

 

Niessen, W.M.A. 2001. Current practice of gas chromatography – mass spectrometry” Marcel Dekker. New York.

 

Pesce, Amadeo (31/03/2011). "Drugs-of-abuse testing and therapeutic-drug monitoring". MLO. Medical laboratory observer (0580-7247), 43 (3), p. 42.

 

Rossi, Riccardo (01/01/2005). "Hair analysis by GC/MS/MS to verify abuse of drugs". Journal of applied toxicology (0260-437X), 25 (3), p. 205.

 

Samyn, Nele (01/08/2007). "Bioanalytical procedures for determination of drugs of abuse in oral fluid". Analytical and bioanalytical chemistry (1618-2642), 388 (7), p. 1437.

 

Thevis, Mario (01/01/2007). "Mass spectrometry in sports drug testing: Structure characterization and analytical assays". Mass spectrometry reviews (0277-7037), 26 (1), p. 79.