Principles of Chromatography - Research Paper Example

Chromatography xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Name xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Course xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Instructor xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Date Table of Contents Table of Contents 1 1.0Title 3 2.0. Abstract 3 3.0 Introduction 3 4.0 Aims 5 5.0 Methods 5 6.0 Results 5 7.0 Discussion 10 8.0 References 13 1.0Title Chromatography is the processes used to separate dyes after exposing pen marks to a solvent that will dissolve the ink. 2.0. Abstract The processes used here is for separating ink pigments with the use of paper chromatography. As the water moves through the paper strip it dissolves the pen ink. The water/alcohol moves past the ink and begins to carry the particles that make the ink up. It is clear that, the lightest colour particles move very fast and covers the longest distance. The process separates all the pigments that make up the ink being tested. It was clearly indicated that, even though a pen may be using a specific ink, that ink is made up of different colours and this processes can be very effective in uncovering criminal activities. 3.0 Introduction Most of the substances that people come into contact with on a daily basis are impure. This means that they are mixtures. Therefore a major focus of research in chemistry is coming up with methods and ways of separating and indentifying components of mixtures (Cai et al, 2007). Many separation methods solely rely on physical differences between the component mixture like where there is the use of filtration, centrifugation and distillation. Chromatography uses the differences in solubility and adsorption. Chromatography is a method that is used to analyze mixtures by separating them into the chemicals they were made from (Warren, 2005) It is derived from Greek words ‘Chromat’ which means colour and ‘graphon’ which means to write. While it is an ink chromatography, one separates the colour pigments that make up the colour of the pen. This entails that, even if a pen write in one color, the ink is made up from a variety of different color pigments (Horrocks, Coulson, & Walsh, 1999). This process can be used to separate ink, blood and gasoline just to mention but a few. Forensic scientists use ink chromatography to solve crimes by matching the documents or stains found at a crime scene to the marker or pen that belongs to a suspect (Gunn, 2009). They then analyze the unknown ink and compare it to writing utensils collected from a possible suspect. When performing this experiment, one puts a dot of ink to be separated at one end of a strip of paper (Wistuba & Schurig, 2001). The end is then placed on a solvent which moves up the paper slip dissolving the mixture of chemicals and pulls them up the paper. The results of this process are referred to as chromatogram. It is worth noting, chromatography involves separation of molecules through the stationary phase and the mobile phase. The stationary phase is the paper while the mobile phase is the solvent used. This being the case, the molecules move through the stationary phase at different rates; meaning that, those strongly attached to the paper move slowly and also those that are large while the small ones move very quickly. Substances can be separated on the basis of pH, polarity or even size (Warren, 2005). This process is actually a process that is used to explore capillary action on how a solvent moves up the paper and chromatography which is how different elements of ink are carried along at different rates. To separate several dyes, one must expose the pen marks to a solvent that will dissolve the ink (Trapp & Schurig, 2001). In this experiment, two solvents are used: water and alcohol. This is due to the fact that some ink is soluble in water and therefore it is used as solvent. Those inks that are not soluble in water are often soluble in alcohol and therefore alcholol is used to separate the dyes. 4.0 Aims The aims of the experiment are to separate mixtures of ink using a thin layer chromatography or paper and calculate Rf values of the separated inks. 5.0 Methods Water of about 10ml was poured into a small cup. A strip of filter paper was cut so as to form a point at the end. A marker was chosen and a good size dot of color made of about 1.5cm up from the pointed end of the paper. A pencil was then used to make a mark on the paper strip beside the ink dot. The pointed end of the paper was then lowered into the solvent but then it was ensured that the dot stays above the solvent level (Silva da, Lima de & Tavarea, 2003). A tooth pick was carefully pushed through the top of the paper to hold the strip at just the right level in the cup. There was a clear indication of ink pigments moving up the paper strip. While waiting for the solvent to rise towards the top of the paper, another beaker/cup was set up to test other markers (Hamada & Wintersteiger, 2002). When the solvent finished moving up the paper strip, the paper was removed from the cup and immediately marked with a pencil the highest point the solvent travelled up the paper strip. The strip was left to dry while it was taped in the reference library page under its correct brand name (Cserháti & Forgács, 2001). This continued until all the ink samples were tested. 6.0 Results In this experiment, paper chromatography was applied in different samples and the components of the mixture characterized. The experiment controls three variables in paper chromatography; solvent, paper and distance covered by the solvent. To repeat this is a tiring task and therefore the ratio called for representative fraction, Rf, is computed (Buo et al, 2001). This representative fraction Rf is therefore calculation as: Rf=distance from centre of spot to starting point/ distance from solvent front to starting point. Figure 7 is a sample chromatograph and shows the quantities in the equation are determined from the experiment. The Rf therefore is independent of the distance the solvent was allowed to move and can easily be repeated. Figure 7 shows how paper chromatography can be used to determine whether a sample is a mixture and also to indentify the components of the sample. For instance, the chromatograph in this figure implies that spot 3 and spot 4 are identical because they both have the same Rf. For spot 2, the results of chromatography for a mixture of compounds; the mixture is clearly separated in to several components and the identity of each clearly established (Beltran, Lope & Hernandez, 2000). When a mixture contains a mixture of two compounds of similar Rf, performing chromatography of such a mixture will not clearly separate. The resolution of a chromatograph can be changed by using different solvent, using different stationary phase or letting the solvent move farther along the chromatogram (Azevedo et al, 2000). This is the case for Fig 9 spots 3, 4 and 5. Fig 1 Chromatography of ink group Fig 2 several spots did not move any further. This is attributed to solubility of their pigments. The elements were too dense to move as fast as the other colours. Fig 3 In this figure, the results show that, there are ink elements that were strongly attached to the paper and therefore they also moved slowly. Fig 4 This result depicts that the elements in this sample moved freely in the filter paper. This is attributed to their attachment to the paper and therefore they moved very quickly. Fig 5 These results depicted that, there are some colours that move at a very high speed in the filter paper. These colours are yellow and blue. This is attributed to their solubility and rightness and thus they don have a strong attachment with the filter paper. Fig 6 One spot moved very fast which contained the black and blue colours. fig 7 this figure implies that spot 3 and spot 4 are identical because they both have the same Rf. For spot 2, the results of chromatography for a mixture of compounds; the mixture is clearly separated in to 6 components and the identity of each clearly established Fig 8 7.0 Discussion The main aim of this study was to indentify an easily applicable method for the analysis of ink components and to avoid any sample loss of analyses and contamination. Pens inks consist of several acids or direct dye components which are mixed proportionally to offer the needed colours (Cserháti & Forgács, 2001). The maximum UV absorption bands of a pen ink were situated between 500 and 700nm and most of the dye components have a minimum absorption nearing 590nm for black inks and 520nm for red inks (Trapp & Schurig, 2001). This therefore entails that, the wavelength of detection was set to be 590 and 520 nm respectively. This is due to that, ink is composed of compounds which can be divided into two fractions: non-coloured and coloured (Beltran, Lope & Hernandez, 2000). By means of the diode array detector the separation is monitored and it is noted that UV/Vis spectra were accumulated over the time of the separation as well. A look at the absorption patterns, the separated compounds can be assigned to either on of these fractions (Cserháti & Forgács, 2001). It is also worth noting that, some inks dyes have organic compounds containing conjugated aromatic rings and are sensitive to light. They must therefore undergo degradation during storage. Exploring the decomposition characteristics of the ink entries under light and normal storage conditions would offer scientific evidence for the determination of them in a suspicious document. This therefore means that, they are also of great importance when it comes to forensic science. An increase in the distance for the separation usually leads to separations with improved resolutions but also increased analysis times (Buo et al, 2001). When time increases, the components of the ink almost gets to baseline separation. In a short time, a pattern of colour appeared on the filter paper as can been seen in the samples. Each colour became a single dye that was in the ink. The distance which they travelled on the filter paper is the physical property of that dye (Cserháti & Forgács, 2001). From the result, it is clear that those dyes that are most soluble travel faster and therefore they record the highest levels on the filter paper. Those that are less soluble in the specific solvent travel slowly and do not reach far on the paper. It was noted that, while using water as a solvent, which is very polar substance, the more polar the colour, the higher it raised on the paper (Buo et al, 2001). After the ink has been separated, the results show clearly patterns that are as a result of the ink pigments that have been separated. In some samples it is very clear for they separation resulted to rainbow patterns (Trapp & Schurig, 2001). In forensic, this can be used to indentify a suspect for instance like the pen which wrote a ransom note in case of kidnapping. 8.0 References Azevedo DA, Lacorte S, Vinhas T, Viana P and Barcelo D.2000. Monitoring of priority pesticides and other organic pollutants in river water from Portugal by gas chromatography–mass spectrometry and liquid chromatography–atmospheric pressure chemical ionization mass spectrometry. Journal of Chromatography A ; 879: 13–26. Beltran J, Lopez FJ and Hernandez F.2000 Solid-phase microextraction in pesticide residue analysis. Journal of Chromatography A; 885: 389–404. Buo Carrasco P, Escola R, Marco M-P and Bayona JM.2001. Development and application of immunoaffinity chromatography for the determination of the triazinic biocides in seawater. Journal of Chromatography A ; 909: 61–72. Cai,S.S Short L.C., Syage J.A., Potvin M., Curtis, J. 2007 Chromatogr. A 1173 88. Cserháti T and Forgács E. 2001 Chromatography in Environmental Protection.Harwood Academic: Australia. Horrocks, M., Coulson, S.A., & Walsh. K.A.J., 1999 ‘Forensic palynology: variation in the pollen content of soil on shoes and in shoeprints in soil’ 1999, Journal of Forensic Science 44, 119-122. Hamada M and Wintersteiger R. 2002. Rapid screening of triazines and quantitative determination in drinking water. Journal of Biochemical and Biophysical Methods; 53:229–239. Gunn A.,2009 Essential Forensic Biology, Second edition, John Wiley&Sons, 2009. Silva da C, Lima de EC and Tavareas. 2003. Investigation of preconcentration strategies for the trace analysis of multi-residue pesticides in real samples by capillary electrophoresis. Journal of Chromatography A; 1014: 109–116. Trapp, O. Schurig, V. 2001.Approximation Function for the Direct Calculation of Rate Constants an Gibbs Energies of Enantiomerization of Racemic Mixtures from Chromatographic Parameters in Dynamic Chromatography" J. Chromatography. A, 911 (2001) 167-175. Warren, J., 2005‘Representativeness of Environmental Samples’, Environmental Forensics, 6, 21-25 Read More