Determination of Specific Functional Groups

The reference spectrum library mentioned above has made it possible to identify & 50 functional groups due to their characteristic spectral appearances. These characteristics allow the assignment of a specific functional group in a compound without access to any reference spectrum. The specific functional groups can, for example, be exposed in a contour plot shown in Figure 6, where the measuring data (second derivatives) for single, double and polyaromatic compounds are outlined quite clearly. Specific chromatograms can be obtained for these aromatic groups by taking the average absorption in appropriate wavelength ranges.

Another example of specific detection is shown in Figure 7, where 6 mg of a dust sample was analysed by means of GC-MS and GC-UV. In both cases the analysis involved a thermal desorption before the gas chromatographic separation and in both cases the same type of capillary column and the same temper ature programme were used. Figure 7A shows the chromatogram from the GC-MS total ion signal and Figure 7B-D shows the GC-UV chromatograms obtained at the wavelength ranges indicated. The chromatograms were calculated using the absolute values of the first derivatives of absorption spectra. Identifications were carried out by means of GC-MS for the peaks indicated 1-5 with following results: (1) hexanal; (2) heptanal; (3) octanal, (4) nonanal and (5) decanal. The nonaromatic straight chain aldehyde group has a characteristic sharp UV absorption edge at 187 nm. Therefore a specific detection of nonaromatic straight chain aldehydes can be made in the 187-190 nm wavelength range, as shown in the figure. The next GC-UV trace shows the chromatogram from the average values in the 187-220 nm range. This gives a less specific chromatogram. Naphthalene was identified at the indicated position (6) by means of a search against the gas-phase UV reference spectra library. The same library was used for the identifications of benzaldehyde at position (7) and 2-furaldehyde at position (8). The spectrum of 2-furaldehyde has a dominating absorption profile between 230 and 270 nm and, consequently, it only appears in the 238-244 nm wavelength trace.

The experiences of combining results from GC-MS and GC-UV have recently been explored and there are indications of valuable possibilities. The characteristic complementary qualities for GC-UV compared to GC-MS allow specific determinations - determinations of specific functional groups and also of structural isomers, which are difficult to distinguish by means of MS.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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