Secondly, they provide the accurate measurements that do not require external calibration. Finally, the methods are easy in exploitation and provide the fast results, define the things that can `t be gathered in the natural way. p align="justify">
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 forens...
