How Is Gas Chromatography Utilised In Identifying Alcoholic Substances In Criminal Investigation?

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How Is Gas Chromatography Utilised In Identifying Alcoholic Substances In Criminal Investigation?

Rationale

Forensic chemistry is the application of chemistry, forensic toxicology, in a legal setting. A forensic chemist can assist in the identification of unknown materials and instruments found at a crime scene. Forensic Chemists have a wide array of methods used to identify unknown substances including High performance liquid chromatography (HPCL), gas chromatography (GC), atomic absorption spectroscopy, Fourier transform infrared spectroscopy, and thin layer chromatography. These different types of methods are important due to the critical nature of some instruments and the number of possible unknown substances that can be found at a crime scene. They prefer using non-destructive methods first, to preserve evidence and to determine which destructive methods will produce the best results. (n.d., 2019) Ethanol, also called alcohol, is a clear liquid and the principle ingredient in alcoholic beverages for example, beer, wine or brandy (ChemicalSafetyFacts.org, 2019). A Breathalyzer is one of a device estimating blood alcohol content from a breath sample (n.d, 2006) Blood alcohol estimation is important as it imparts an ability to perceive individualized impairment that may present under the legal limit for driving. Therefore, the training can be a useful component for moderate drinkers in drunk driving prevention programs (Aston and Liguori, 2012). This research task will further explore the analysis of alcohol specifically using gas chromatography. Research QuestionHow is gas chromatography utilised in identifying alcoholic substances such as ethanol in blood and hence crucial in criminal investigation?

This review will use three studies from Tangerman (1997), ebook from US (n.d), and Tiscione et al. (2011) that have been undertaken to determine the detecting and identifying of ethanol by using Gas Chromatography. The results of these studies will be complied to investigate the analysis of ethanol using Gas Chromatography.

Analysis and Interpretation

Background

Chromatography is a technique that enables the separation and identification for qualitative or quantitative analysis based upon their differential distribution between two phases: stationary and mobile phases. Stationary phase: different strengths of attachment. Mobile phase: different solubilities in solvent being used. Both phases can be identified in a mixture and determined how much of each is present. Retention time: a measure of the time taken for a solute to pass through a chromatography column. It is calculated as the time from injection to detection. (Chromatography Today, 2014) There are different types of chromatography including gas, liquid, column, paper and high-performance liquid etc. (DayMap, 2019). Affinity chromatography is one of chromatographic methods for purification of a specific molecule from a complex mixture (Urh M, 2009).

Carrier gas introduced from a gas cylinder outside the machine. It carries the sample through the machine – carrier gas is the mobile phase. The rate of flow of the carrier is controlled, giving the clearest separation of the components in the sample. Once a sample of the mixture of substances in a syringe and injected into the machine. The carrier enters the machine through a column. The components of the mixture are heated, instantaneously vaporise, the sample separate out as they move through the column – stationary phase. The column is a metal tube and entirely contained inside an oven, keeping at a high temperature, ensuring that the sample remains in a gas form. As the sample separates out, its component gases travel through the column at different speeds, an electronic detector sense and record them. Finally, the data analyser attached to the machine illustrates a chart that has a series of peaks that correspond to all the substances in the mixture (Woodford, 2018).

Review of the result

In the experiment of determination of alcohol (ethanol) by using gas chromatography to the separation of a water-ethanol mixture. It is used when law enforcement agencies need to determine whether or not someone is intoxicated. High sensitivity required 0.1% blood alcohol is legally intoxicated in most states. Determination will deal with higher concentrations (up to 25% by volume) which are more typical of alcohol levels found in many alcoholic beverages. Gas chromatography is an effective method for the separation, identification and quantitation of components in a mixture.

Monitoring

Ethanol can be monitored to determine the proof value of the alcohol beverage, while methanol and isopropanol can be measured to determine the levels of denaturants present. While poor methanol peak shapes often are associated with columns of limited sample volume and sized packed column with 5% Carbowax® 20M provides peak shape for methanol, and completely resolves methanol from ethanol. From the graph above, it shows the difficulty to monitor of ethanol is very high compared to the rest.

The peak of acetaldehyde at the retention time at 0.36 min was separated from ethanol (at retention time of 0.43 min) at a column temperature of 120 °C. Ethanol, methanol, and acetone were accorded at 120 °C. A baseline separation between acetaldehyde, methanol, acetone, and ethanol was found at a column temperature of 60 °C. Some forensic important congeners of ethanol showed baseline separation at 60 °C. No carryover problems were seen for ethanol, and not for any of the other volatiles studied. (Tangerman, 1997).

Calibration for ethanol HYPERLINK ‘https://d9aqs07uebq07.cloudfront.net/content/clinchem/43/6/1003/F4.large.jpg?width=800&height=600&carousel=1’ o ‘The calibration curves for ethanol in water (y = 50 157x + 5929, r = 0.9996), whole blood (y = 50 728x 1036, r = 0.9991), serum (y = 48 676x + 2518, r = 0.9999), urine (y = 49 929x + 4012, r = 0.9998), and fecal water (y = 51 059x + 3225, r = 0.9997).Column temperature: 120 °C; injection volume: 2.0 ¼L.’

Daily calibration was performed with the aqueous ethanol calibration solutions with a concentration of 15 g/L. A linear correlation was obtained between concentration and area of the peak. There was not a lot difference between the relationship of the calibration line of ethanol in water and ethanol in blood, serum, urine, and fecal supernatant. The biological matrix did not influence the GC analysis. Although, the calibration curves were also linear in the low concentration range (0.00010.5 g/L) (Tangerman, 1997).

Correlation between the instrument responses for blood and urine were compared to aqueous by plotting the instrument response and evaluating the coefficient of determination of the resulting curve. The linear calibration curves that were generated for the aqueous, urine, and blood. Linearity was further investigated by analysing a second set of ethanol prepared in deionized water by three different analysts in three different days. All three calibration curves from 0.010 to 1.000 g/dL generated r2 of 1.000. The calibration range used was evaluated throughout the validation process by analysing the Cerilliant calibrators at concentrations of 0.020, 0.100, 0.200, and 0.500 g/dL 18 times on 18 different days of 4 different analysts. The concentration of all calibrators in all experiments was within 0.005 g/dL or 5% of the target concentration. From 0.010 to 1.000 g/dL, shown to be linear. The calibration curves generated from each matrix were virtually identical when comparing the slope, y-intercept, and r2.

From the results collected, it is concluded that Gas Chromatography is a quantitative analysis. According to USC Libraries, quantitative analysis emphasises objective measurements and the statically of data collected using computational techniques (). which means that data, which represent the graphs that as generates numerical data is quantitative analysis. However, According to Sciencing, qualitative analysis is a method of analysing organic and inorganic substances or in another word, it generates non-numerical data. For this investigation, the technique chosen comprises of only quantitative analysis as they are representing results in numerical data (graphs), within the results. Comparing the sources, data, monitored to determine the proof value of the alcohol beverage and data, motoring of the retention of detector responses to each components. Calibration curves for ethanol in water, whole blood, serum, urine, and fecal water, and calibration of ethanol in three matrices: aqueous, urine and blood. Overall, Gas Chromatography is a confirmatory test.

Conclusion and Evaluation

In this investigation, three literature sources were chosen in an attempt to ensure consistency of the results explore the use of Gas Chromatography to identified ethanol in alcohol. Tangerman (1997), and Tiscione et al. (2011) contained detailed experimental procedures. However, these three resources used different volume, concentration and temperature when conducting the test. This limits the ability to compare the results of the studies, only their conclusion can be used. Ebook from US (n.d) contains no detail of the preparation of the solution, the concentration of solution and the methods used to determine the results. This doesnt provide clarity in how does gas chromatogray can be used to identify ethanol in criminal investigation. This paper, therefore, doesnt add value to the discussion.

Overall Results

The three studies were used to exploring the analysis of alcohol by using gas chromatography. Data collect were using different volume, concentration and temperature in the experiment. It was resulted that ethanol was the hardest substance to monitor, ethanol separated (0.43 min) at a column temperature of 120 °C, no significant differences were observed between the calibration line of ethanol in water and those of ethanol in blood. Lastly, data representing correlation between the instrument responses for blood and urine were compared to aqueous by plotting the instrument response and evaluating the coefficient of determination of the resulting curve.

Further Investigation

To truly investigate how gas chromatography used to identifying ethanol in criminal investigation, further examination needs to be carried out. This testing would need to use the same Gas Chromatography materials and instruments, a larger sample, no. of trials, and use the same sample, concentration, volume and column temperature throughout the experiment. They would need to remain constant in all testing. As this would increase the reliability and validity of the result. The difficultly of monitoring the substances (i.e from the driver) could be investigated more.

For the extension, as mentioned in the rationale, there are many different types of chromatography, the investigation of this would be to use the same sample and carrier gas but use different types of chromatography. Ethanol is a good analyst for gas chromatography as it is the most common analyte identified in forensic toxicology laboratories. This will prove how each of the Chromatography utilised in identifying alcoholic substances such as ethanol in criminal investigation. This will support the claim that Chemical analysis is an important aspect of criminal investigation.

Reference list

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