As a forensic chemist who has been assigned to analyze any items collected at a crime scene, I will first attempt to investigate the article in the plastic bag. According to the police report, the crime scene sample was possibly discarded during a police chase. The item is a plastic bag that was lying on the ground and was opened. The plastic bag contained a powdery substance of off-white color, as well as dark particles similar to the color of soil. The police officers suspect that the content of the plastic bag was a narcotic drug.
My initial task as a forensic chemist is to determine the physical properties of the chemical substance in the plastic bag. Physical properties include the color, texture and possibly, density. Based on my own perspectives, the content of the plastic bag is the same as that reported by the police officers as an off-white powdery substance that is mixed with dark-colored granules similar to that of soil particles. Another task that I would perform is to determine the smell of the substance.
Each chemical has a particular scent and I can perform this by simply wafting my hand above the powdery substance and checking whether there is a peculiar smell that is specific to a particular chemical substance. The next task I would perform is to determine the chemical properties of the substance. I will take a small amount of the off-white powdery substance and determine its weight, after which I will dissolve this in 1 millimeter of distilled, deionized water and check for its pH level. I may use either a pH strip or a pH meter to perform this task.
Determination of the pH level of the solution containing the powdery substance dissolved in water will provide me an idea if the substance is an acid, a base or a neutral compound (Grim et al. , 2001). If the pH level of the solution is less than 7, then the powdery substance is an acid. On the other hand, if the pH level of the solution is above 7, then the powdery substance is a base. A pH level reading of 7 will let me know that the powdery substance is a neutral chemical (Grim et al. , 2002). I will also conduct the scientific method on the forensic analysis of the powder present in the plastic bag.
The scientific method is composed of a series of steps from the observation of the test sample to the generation of a hypothesis on the possible identity of the powder. The hypothesis is then tested through a series of experiments that will help me determine that exact identity and composition of the powder. Knowing that the test sample here is powder, I will also perform microscopy analysis of the crystals of this substance. I would employ a brightfield microscope that is equipped with phase contrast optics so that I will not need any special stains to view the powder at high resolution.
Visualization of the powdery substance under high-powered lenses will provide me a way to look closely at the crystals that make up the powder. It may provide me information of the shape of the crystals, whether these are stellate in shape, or cuboidal or spherical. I can then compare the observed shape of the crystals with any documented powder description for additional information that may lead me to the identity of the test sample. After determining the physical properties of the powder, I will then proceed to the next task of determining the identity of the substance.
It should be noted that each chemical substance carries a unique set of properties that may not be so obvious through visual inspection or simple chemical testing such as pH determination or dissolution in particular reagents. In this particular task, I will perform two types of analyses. The previous analyses mentioned were all presumptive, which means that the information that I have gathered does not pinpoint the exact identity of the powder but simply rules out general features of a certain category of reagents.
For example, the determination of the pH level of the powder will help me rule out that the substance is not basic or acidic. Another form of analysis for the identity of the powdery substance is to perform confirmatory tests (Lidgard and Duncan, 1995). Therefore another task that I would perform would include testing a small portion of the powdery substance for its reaction to specific chemical reagents. For example, I can take a small amount of the powder and introduce this to cobal thiocyanate, which is known to react by generating bubbles.
The creation of bubbles will let me know that the off-white powder is cocaine (Mule and Gasella, 1989). Another confirmatory test that I would perform is that to determine whether the powdery substance is methamphetamine. This narcotic drug is known to react to a specific reagent such as sodium nitroprusside (Taylor and Le, 1989). However, the reaction can only take place when sodium bicarbonate is also added to the mixture. A confirmatory result for methamphetamine will show that the addition of sodium nitroprusside and sodium bicarbonate to the powdery substance will generate a dark blue solution.
Therefore, if I perform this confirmatory test on the powdery substance and I get the blue coloration in the mixture, then the powdery substance in the plastic bag is methamphetamine (Gjerde et al. , 1993). However, I should also be cautious with this confirmatory test because there are still a number of substances that will result in a dark blue color when sodium nitroprusside and sodium bicarbonate are added to an unknown substance. The reaction of creating this dark blue color occurs in several other chemical substances because of the presence of a structural similarity in their chemical structures.
The common structure present in these reagents is composed of nitrogen, hydrogen and two carbon atoms. The presence of this consensus structure will thus produce the same dark blue-colored solution after adding sodium nitroprusside and sodium bicarbonate. Yet it is still helpful to perform this test because it further helps me decrease the number of possible chemicals that I would consider for my identification. Another task I would perform for the identification of the powdery substance is to conduct Fourier transform infrared (FTIR) spectrophotometry.
In this procedure, the actual interaction of the unknown powdery substance can be determined through readings using infrared light (Burns and Doolan, (2005). The mode of interaction is calculated from the wavelength of the light hitting the chemical substance and this is also called the chemical fingerprint (Conneely et al. , 2001). The phrase was coined in order to describe that the interaction pattern that results from the infrared illumination is unique to a particular chemical and will not be the same as another chemical (Gratz et al. , 2006).
The FTIR spectrophotometry is thus a helpful technique in verifying the identity of a chemical substance (Suzuki, 1998, 1999). In the case wherein the substance may be made of several compounds, another confirmatory test should be performed in order to determine each constituent of the powdery substance. As a forensic chemist, I will then also perform gas chromatography-mass spectrometry (GC-MS), which involves the separation of chemical constituents in a solution or mixture. The process of separation is based on the principle of chromatography, wherein each chemical migrates according to its chemical weight.
A substrate for migration is also employed in this procedure and in GC-MS, the unknown chemical substances are transformed into their gaseous phases for migration and eventual identification through the molecular mass (Balko and Allison, 2003). GC-MS results generally include graphs, which show defined peaks that identify a certain component of a substance, including its molecular weight (Hobbs and Almirall, 2003). Thus if two peaks are shown in the GC-MS graph, this will mean that the unknown powder is composed of two main chemicals (Kim et al. , 2008).
If there is only one peak in the GC-MS graph, then the powdery substance is in its pure form (Hornbeck et al. , 1993). The GC-MS equipment is also capable of identification the exact chemical substance that is in the sample capillary (Putzbach et al. , 2007). Each capillary is loaded into the GC-MS and run for separation and identification of chemical constituents (Kosevich et al. , 1994). I will also perform comparative assays that will help in determining whether the powdery substance is similar or different to a known chemical reagent (Sakayanagi et al. , 1999).
The comparative analysis will also facilitate in the classification of the unknown powder. Aside from the classification, I will also perform an analysis of the variation of the unknown powder in order to establish the origin of the forensic sample (Flynn et al. , 2005). I would also want to determine the difference of the forensic sample from the rest of the reported and available samples, so that I may explain how the unknown powder was derived or generated (Morkved et al. , 2002).
It may be possible that the methamphetamine that was in the plastic bag is a commercial one and through the analysis for variation I can verify this. I can also verify if the potential methamphetamine is home-made. As for the clothing of the suspect, the presence of the same substance can be checked from GC-MS. The clothes of the suspect can be soaked in water and the water solution can be subjected to GC-MS in order to determine whether the same powdery substance was present in the suspect’s clothing.
If a positive match is made, then we can confirm that the suspect carried the powdery substance during the police chase. The plastic bag can also be checked for fingerprints and this should be matched with the suspect’s fingerprints. Any DNA samples should also be checked in the plastic bag and compared with the DNA fingerprint of the suspect. If there is a positive match between the DNA profile of the suspect and that of the DNA profile collected from the plastic bag and its contents, then this strongly proves that the suspect is the owner of the plastic bag that contained the powdery substance.
Forensic analysis is a very powerful and reliable method in investigating crime scenes. However, there should be extreme caution in conducting any identification and analysis of crime scene items and evidences because it is also possible that the wrong or misguiding procedure was performed and that erroneous results could declare a suspect guilty. Forensic chemistry is one of the specialized fields of forensic science and it is important because it provides information on the identity and properties of any unknown material or substance that is collected at a crime scene.
References Balko L & Allison J. (2003). The direct detection and identification of staining dyes from security inks in the presence of other colorants, on currency and fabrics, by laser desorption mass spectrometry. Journal of Forensic Science, 48,1172–1178. Burns DT & Doolan KP. (2005). A comparison of pyrolysis-gas chromatography–mass spectrometry and Fourier transform infrared spectroscopy for the characterization of automotive paint samples. Analytica Chimica Acta, 539,145–155.
Conneely A, McClean S, Smyth WF & McMullan G. (2001). Study of the mass spectrometric behaviour of phthalocyanine and azo dyes using electrospray ionisation and matrix-assisted laser desorption ? ionisation. Rapid Communications in Spectrometry, 15,2076–2084. Flynn K, O’Leary R, Lennard C, Roux C & Reedy BJ. (2005). Forensic applications of infrared chemical imaging: Multi-layered paint chips. Journal of Forensic Science, 50,832–841. Gjerde H, Hasvold I, Pettersen G & Christophersen AS. (1993).
Determination of amphetamine and methamphetamune in blood by derivatization with perfluorooctanoyl chloride and gas chromatography mass spectrometry. Journal of Analytical Toxicology, 17:65-68. Gratz SR, Gamble BM & Flurer RA (2006). Accurate mass measurement using Fourier transform ion cyclotron resonance mass spectrometry for structure elucidation of designer drug analogs of tadalafil, vardenafil and sildenafil in herbal and pharmaceutical matrices. Rapid Communications in Mass Spectrometry, 20,2317–2327.