This purpose of this lab is to use gas chromatography to identify unknown compounds. In this lab, six known substances were first tested for their retention times to be used as standards when figuring out the three substances contained in a known mixture. The vernier mini gc in this experiment, just like all the other types of chromatography, have both a stationary and mobile phase. With this instrument, the stationary phase is a metal outer column and the mobile phase is the atmospheric air, which is how the vernier mini gc works. This instrument is used alongside a computer to be able to obtain the readings of the injected substances and shown as peaks on a chromatograph. The specific time it takes for a substance to exit the chromatography
When observing the gas chromatography curves, it was evident that there were two pentenes in the unknown mixture, GC_7. This is due to the two peaks on the graph with retention periods (minutes) of 2.802 and 2.883 for the first and second peaks, respectively. The area under the first peak was 36 (m2) and the second was 164 (m2). The compound affiliated with the first peak was 18% of the whole mixture. The compound affiliated with the second peak was 82% of the whole mixture. The theoretical plate for the first peak was 7.851 and the second peak was 8.312. The resolution of these two compounds was 0.0205. Ultimately, the data collected gave a result to indicate there was clearly two prominent compounds that compose the unknown mixture.
Forensic Chemistry involves a variety of different techniques in which have the ability to analyse samples found on crime scene, one set of techniques is that of chromatography.
By Using specific methods of compounds detection, we can match an unknown compound with a known compound because similar compounds will display similar characteristics. In this experiment, identifications of the unknown ketone was accomplished using thin layer chromatography, melting point, and NMR spectrometry. Thin layer chromatography is very quick but sensitive way of determining the components of a mixture or a specific compound from a list of knowns. This method is the one which was utilized in the
The introduction of the modern use of fingerprinting all started in 1984, when a British geneticist named Alec Jeffreys came across new methods for DNA fingerprinting (Jones, 2012). Since his discovery, this technique has been used successfully to identify perpetrators of crimes. For more than a century in fact, fingerprints have been used as identification tools by law enforcement. Known as “friction ridge analysis,” (Jones, 2012), this forensic method comprises of examiners comparing details of an unknown print against known prints. These details are analyzed
At a crime scene, the one thing that can never be fully covered up is the presence of finger prints. Because of the oils we produce through our skin, our fingers leave prints on any imaginable surface, including on another body. These finger prints are classified in many different ways in order to make the extraction, storage and eventual cross-reference of these fingerprints much easier for future analysis purposes. The
Fingerprints have been used for a very long time, as far back as 3,000 years ago in China as identification. The use of ancient fingerprints are not the same techniques we use today. In 1880, a man by the name of Henry Fauld, “a Scottish physician working in a hospital in Japan, published his own views on the potential application of fingerprinting to personal identification” (Saferstein, 2016, pg. 164). He suggested that the skin patterns could be important for the identification of criminals. After comparing different fingerprints, he began to realize that each print looked remarkably different. Fauld believed that fingerprints could be used as evidence and suggested the proposal to a fingerprint testing center, but the offer was rejected. Years later, the first prosecution fingerprints were used in the year 1905 in London (Rotella, Abbott, & Gold, 2001). Ever since then fingerprints have been a valuable part of crime scene investigations and if present, it is almost guaranteed that the criminal will fit the crime. It has been a successful technique that has proved more success than any other piece of evidence.
The primary goal of this laboratory is to correctly identify an unknown substance. To achieve this task, one may use various tests that reveal both chemical and physical properties of a substance. By comparing the results of a known substance and the unknown substance, one may eliminate alternative possibilities and more accurately predict the undisclosed compound. Furthermore, by performing these tests, data can be collected and verified regarding chemical and physical properties of the unknown. Understanding the chemical properties of a known substance aids one’s understanding of the unknown based on comparative analysis of the results of the tests.
Howlett, S. E. and Steiner, R. R. 2011. Validation of Thin Layer Chromatography with AccuTOF-DART™ Detection for Forensic Drug Analysis*. Forensic Sciences [e-journal] 56 (5), pp. 1261--1267. Available through: Anglia Ruskin University Library website http://libweb.anglia.ac.uk [Accessed on 11 March 2014].
By correlating the retention time of pure compounds to the retention time of the sample, the compound in the sample can be identified. As seen in Figure 1, there were 2 peaks seen in the GC graph, which indicates there were 2 compound made up in the product. Since cyclohexane was added into the product, it is safe to assume that the peaks were cyclohexane and bromocyclohexane. According to table 2, their retention times were 2.469 and 2.780mn, respectively from 1-2. The first peak was most likely to be cyclohexane since it is less polar compared to bromocyclohexane; therefore, the nonpolar compound will come out first at 2.469mn. If so, the second peak that came out second at 2.780mn was surely bromocyclohexane, the wanted product. According to both figure 1 and table 2, cyclohexane was responsible for 73.78% of the total sample used for analysis whereas bromocyclohexane only accounted for 26.22%. Even though the graph suggested the product was pure when the cyclohexane was neglected, some bumps could be seen within range of 3 to 4mn, which indicated that the product was not 100%
The smaller the alkane the faster it will reach the detector, therefore the shorter the retention time. This is because alkanes experience intermolecular Van-der-waal forces. The stronger these forces are the greater the boiling point of the alkane. The larger the alkane, the more Hydrogen bonds there are, meaning they have stronger forces (and a higher boiling point). Components with low boiling points travel faster through the column than higher boiling points, therefore the retention time of Octane is 1.25 min while the retention time of Dodecane is 5.50 min.
In quadrants 1 and 2 how the amount and constituents of the fingerprint residue on the substrate affects the fingerprint image, is determined. In quadrant 1, excess sebum and moisture is first removed from the finger tips with the help of a clean cloth. In quadrant 2, fingertip is first wiped around the nose or forehead to create excess sebum. Quadrant 3 and 4 were used to compare the details between untreated and dusted fingerprint residues.
Every time somebody touches something, they leave behind a unique signature that forever links them to that object. This link is their fingerprints, which are unique to every person, for no two people have the same set, not even family members or identical twins. Palms and toes also leave prints behind, but these are far less commonly found during crime scene investigations. Therefore, fingerprints provide an identification process that is applicable to background checks, biometric security, mass disaster identification, and most importantly, crime scene investigations. Fingerprints are so differentiated because they are made up of distinct patterns of ridges and furrows on the fingers. The ridges are the “raised” portions of the prints, and the furrows are the “recessed” portions. This perceived uniqueness has led some people to falsely accept fingerprint analysis as absolute scientific fact. Although overall fingerprints are reliable, there are definitely situations where their accuracy can come into question.