A critical evaluation of infrared analysis and mass spectrometry in forensic science
Сочинение - Медицина, физкультура, здравоохранение
Другие сочинения по предмету Медицина, физкультура, здравоохранение
be gathered in the natural way.
comparison of Infrared Analysis and Mass Spectrometry
spectroscopy, to be more precise Fourier Transform Infrared Spectroscopy (FTIR), uses the mid-infrared region and this analytical tool probably yields the most information in forensic paint analysis (Chalmers & Griffiths, 2002). Despite this however, FTIR can lack in selectivity. It may not always be easy to discriminate within a particular class especially if a mixture of these is present (Siegel et al., 2000). For example FTIR is not able to discriminate between the plasticizers diisooctyl phthalate and dihexyl phthalate both separately and as a mixture (Siegel et al., 2000). FTIR is also a very sensitive technique. An infrared (IR) spectrum can be collected in a couple of seconds and with repeated scans, the signal-to-noise ratio is increased (Felgett Advantage) (Settle, 1997). This sensitivity feature of FTIR can be said to apply not only to paint analysis but also for any other forensic use. Limitations that an FTIR has are that elemental information is very limited, molecule/s must be IR active and the matrix the molecule of interest is present with must be transparent to IR (Settle, 1997). The latter limitation has a direct effect on selectivity. If the matrix is not IR transparent the IR spectrum would be a mixture and selectivity would be low (Boon & Learner, 2002). Mass spectrometry makes use of ionized particles in order to measure their mass-to-charge ratio (m/z). Despite its wide range of application and advantages in forensic science, one of the main limitations of mass spectrometry is that if the sample is a mixture, the mass spectrum would be likewise (Siegel et al., 2000). To increase selectivity, a modification to the conventional mass spectrometry has been devised: direct temperature-resolved mass spectrometry (DTMS) (Boon & Learner, 2002). Boon & learner (2002) showed in their studies that DTMS can be applied for small samples of paint made up of pigments and organic media. Compounds in paint are physically separated due to their different physical and chemical properties (Boon & Learner, 2002). Sensitivity of mass spectrometry can be increased by making use of the selected ion monitoring (SIM) feature of the mass spectrometer instead of the full scan mode feature (Ekman, Silberring, Westman-Brinkmalm, & Kraj, 2009). Scanning decreases sensitivity as this feature detects ion species one at time (Ekman et al., 2009). Some features that are discussed here with respect to paint analysis of both FTIR and mass spectrometry may also apply to other forensic application., with the help of mass spectrometry can be determined the trace elements in solution. The method provides better sensitivity in comparison to graphite furnace AA. After analyzing mass spectra to ICPOES, the general solution can be made that the mass spectra is much simpler in usage. Even though, the heavy elements provide thousands of emission lines, they include near 1-10 natural isotopes in mass spectrum. Thus, the mass spectrometry has the super sensitivity (Hits, Ronald A, 1992). Infrared analysis has near 2% of the sensitivity limit. However, using the most new techniques its level can be near 0.01%. Mass spectra`s sensitivity depends mostly on the ionization method, thus, an extract with 0.1 to 100 nag may be needed for injection a sufficient amount (Karate, Francis, Ray, Clement, 1988). With the help of infrared analysis the information about positional isomers can gathered, that is not possible using the mass spectrometry method. However, IR in the comparison to MS is less sensitive for 2 to 4 orders of magnitude usually. Analyzing its selectivity, it can be said, that the mass chromatograms can be used as a strongly selective gas detector What is more, MS gives the possibility to gain the additional information on the molecular structure (Griffins, Haseth, 1986), that can`t be provided by the infrared spectra. That is why; the mass spectrometry method is more selective. According to the accuracy, MS uses isotopic internal standards and has the accuracy of 20%. The method is leaded by the general analytical calibration. IR accuracy is 5% in routine analysis. However, in the preferable conditions it can be 1% (Hits, Ronald, 1992). The amount of time that is wasted to prepare the elements in MS method is between 20 and 100 min, to provide the general analysis can take from 1 to 20 hours depend on the elements. To prepare the elements for IR method can tale from 1 to 10 min and to evaluate them - 5 min maximum (Griffins, Haseth, 1986).conclude, both techniques are very helpful in the forensic study. On the one hand, MS is more analytical technique. It is more sensitive and selective. On the other hand, IR is more accurate and spent less time to make the analysis.
Work Cited
infrared spectrometry isomers
1.Boon, J.J., & Learner, T. (2002). Analytical mass spectrometry of artists' acrylic emulsion paints by direct temperature resolved mass spectrometry and laser desorption ionisation mass spectrometry. Journal of Analytical and Applied Pyrolysis , 327-344.
.Chalmers, J.M., & Griffiths, P. R. (2002). Handbook of Vibrational Spectroscopy. Chichester: John Wiley & Sons Ltd.
.Ekman, R., Silberring, J., Westman-Brinkmalm, A. M., & Kraj, A. (2009). Mass Spectrometry: Instrumentation, Interpretation, and Applications. New Jersey: Wiley.
4.Fenn, J.B.; Mann, M.; Meng, C. K.; Wong, S. F.; Whitehouse, C. M. (1989). "Electrospray ionization for mass spectrometry of large biomolecules". Science 246 (4926): 64-71. Bibcode
.Griffins P. R.,J. A. de Haseth (1986) Fourier Transform Infrared Spectrometry. New York: Wiley.
.Hits, Ronald A., (1992). Handbook of Mass Spectra Environmental Contaminants, 2nd ed. Boca Raton, FL: Lewis Publishers.
.J.W.W. Gothard, C. M. Busst, M.A. Branthwaite, N. J. H. Davies and D. M. Denison (1980). "Applications of respiratory mass spectrometry to intensive care". Anaesthesia 35 (9): 890-895
8.Karate, Francis W., Ray E. Clement.( 1988 ). Basic Gas Chromatography-Mass Spectrometry: Principles & Techniques. Amsterdam: Elsevier.
.Kohli, K.; Davies, Gordon; Vinh, N.; West, D.; Estreicher, S.; Gregorkiewicz, T.; Izeddin, I.; Itoh, K. (2006). "Isotope Dependence of the Lifetime of the 1136-cm-1 Vibration of Oxygen in Silicon". Physical Review Letters 96 (22): 225503. Bibcode
.Mukamel S. (2000). "Multidimensional Fentosecond Correlation Spectroscopies of Electronic and Vibrational Excitations". Annual Review of Physics and Chemistry 51 (1): 691
.N. Demirdцven, C.M. Cheatum, H.S. Chung, M. Khalil, J. Knoester, A. Tokmakoff (2004). "Two-dimensional infrared spectroscopy of antiparallel beta-sheet secondary structure". Journal of the American Chemical Society 126 (25): 7981
.P. Hamm, M.H. Lim, R. M. Hochstrasser (1998). "Structure of the amide I band of peptides measured by femtosecond nonlinear-infrared spectroscopy". J. Phys. Chem. B
.Paula, Peter Atkins, Julio de (2009). Elements of physical chemistry (5th ed. ed.). Oxford: Oxford U.P. pp. 459.
.Price, Phil (1991). "Standard definitions of terms relating to mass spectrometry. A report from the Committee on Measurements and Standards of the American Society for Mass Spectrometry". Journal of the American Society for Mass Spectrometry 2 (4): 336-348.
.R.E. March (2000). "Quadrupole ion trap mass spectrometry: a view at the turn of the century". International Journal of Mass Spectrometry 200 (1-3): 285-312.
.Rena A. Sowell, Stormy L. Koeniger, Stephen J. Valentine, Myeong Hee Moon and David E. Clemmer (2004). "Nanoflow LC/IMS-MS and LC/IMS-CID/MS of Protein Mixtures". Journal of the American Society for Mass Spectrometry 15 (9): 1341-1353.
.Schwartz, Jae C.; Michael W. Senko and John E.P. Syka (2002). "A two-dimensional quadrupole ion trap mass spectrometer". Journal of the American Society for Mass Spectrometry 13 (6): 659-669
18.Settle, F.A. (1997). Handbook of Instrumental Techniques for Analytical Chemistry. New Jersey: Prentice Hall.
.Siegel, J.A., Saukko, P.J., & Knupfer, G.C. (2000). Encyclopedia of Forensic Sciences. San Diego: Academic Press.