After CSI technicians have recovered suspicious material evidence like a possible accelerant at a crime scene suspected as arson, they bring it back to the crime lab and look at the evidence more closely. The scientific procedures used in an actual crime lab are similar to those you see on the CSI TV shows. In this article, we will discuss some of the procedures used when CSI technicians examine evidence in closer detail.
In a scientific crime lab, the following procedures are used to analyze compounds up close:
- Gas chromatography
- Mass spectroscopy, and
- Infrared spectrophotometry
No doubt, you may have heard of these terminologies when watching your favorite CSI program.
Gas chromatography (GC) is a method used to identify what a compound is and how far each part of it moves through an inert gas, or noble gas. GC very quickly separates mixtures of compounds into individual parts in this way.
The way GC is performed is that a lab technician injects a liquid sample into one end of the column that is heated and vaporized. The vapor enters the column and flows with the moving inert gas until it reaches another gadget called a detector. Different compounds move at different speeds and thus separate from each other. During this change, the individual compounds arrive at the detector at different times. It is a scientific marathon for individual compounds. The detector then signals another gadget called a recorder that prints a graph, called a chromatograph, that denotes each of the compounds detected. Many times, the result of the GC are needed by technicians to determine the composition of the unknown substance. If they need more information, technicians can combine the results of the GC with the results of either infrared spectrophotometry or mass spectroscopy.
Mass spectroscopy (MS) is another technique used in a crime lab to determine a substance's chemical makeup. Since no two substances have the exact same chemical makeup, or chemical fingerprint, this gadget can be used to determine the makeup of one substance and compare it to another.
The mass spectroscope is a machine that showers a compound with a beam of high-energy electrons that cause the separation of that compound. The resulting individual fragments then pass through an electric or magnetic field that separates them according to their individual masses. The pattern of fragmentation of the unknown compound is then compared via computer to known patterns of fragmentation on record and scrutinized by a technician with the hope of determining a consistency that unveils the composition of the unknown compound.
The GC and MS can be used together. This conglomerate is called a gas chromatograph-mass spectrometer. The GC feeds each separated gaseous substance into the MS which in turn determines the substance's mass spectrum. Just about any substance can be identified using this combination.
Finally, infrared spectrophotometry (IR) is a technique used to identify the absorption spectrum of a compound since each compound has a unique infrared absorption spectrum. This method determines the amount of infrared light absorbed by the compound of interest and results in a chemical fingerprint of that same compound.
IR can also be used in conjunction with GC, and the GC-IR combination very quickly gives results that are just as accurate as the ones given by the GC-MS combination.
Interpreting the Results
Even though technicians can not always determine the exact manufacturer of a given compound, a comparative analysis between the unknown compound and those taken from suspected areas may help them trace the unknown sample to a particular gas station or hardware store that sells the accelerant.
Though this particular investigative technique is not totally reliable, the investigative criminal scientist may be able to say that it came from a particular source.
The next time you watch any of the CSI shows, you will have better knowledge of what some of these techniques are used for whenever you hear the terminologies we have discussed.
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