From Wikipedia, the free encyclopedia
Forensic chemistry is the application of chemistry to law enforcement or the failure of products or processes. Many different analytical methods may be used to reveal what chemical changes occurred during an incident, and so help reconstruct the sequence of events.
One instrument is the gas chromatograph-mass spectrometer (GCMS), which is actually two instruments that are attached. The gas chromatograph is essentially a very hot oven holding a hollow coiled column. A drug sample is diluted in a solvent (e.g.: chloroform, methanol) and is injected into this column, the solvent will evaporate very quickly leaving the drug to travel through the column. Different substances are retained in the column for different amounts of time. The retention time, as compared to a known standard sample using the same method(same column length/polarity, same flow rate, same temperature program), can help to provide a positive identification for the presence of a compound of interest. The column eluant is then fed into a mass spectrometer. A mass spectrometer bombards the eluant with electrons, causing it to fragment into ions. These ions are separated by their mass, commonly with the use of a quadrupole mass analyzer or quadrupole ion trap, and detected by an electron multiplier. This provides a fragmentation pattern, which functions as a sort of fingerprint for each compound, and is compared to a reference sample.
Another instrument used to identify controlled substances is Fourier Transform infrared spectrophotometer (FTIR). The FTIR records the bending and stretching of molecular bonds that are exposed to infrared light. The molecular bonds of all compounds react differently and create unique patterns upon exposure to a beam of infrared light. The unique pattern created is known as the fingerprint for that drug. As with the GCMS the results of the FTIR are compared to a known drug sample, thus producing a definitive identification.
There are two usual pathways into forensic chemistry: through law enforcement, and through science.
Common strands of science applied in the forensic field include analytical chemistry, biology, industrial chemistry and organic chemistry.
The transfer from law enforcement to forensic science is possible, however less likely due to the high costs of training a police office in the field of chemistry.
Forensic chemists usually perform their analytical work in a sterile laboratory decreasing the risk of sample contamination. In order to prevent tampering, forensic chemists must keep track of a chain of custody for each sample. A chain of custody is a document which stays with the evidence at all times. Among other information, contains signatures and identification of all the people involved in transport, storage and analysis of the evidence.
This makes it much more difficult for intentional tampering to occur, it also acts as a detailed record of the location of the evidence at all times for record keeping purposes. It increases the reliablility of a forensic chemist's work and increases the strength of the evidence in court
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