Thin-layer chromatography infrared techniques

The conventional approach to solvent extraction is the batch method. Early work with this method was hampered by the low concentration of the compounds present and the relative insensitivity of the methods of characterization. Thus lipids and hydrocarbons have been separated from seawater by extraction with petroleum ether and ethyl acetate. The fractionation techniques include column and thin-layer chromatography with final characterisation by thin-layer chromatography, infrared, and ultra-violet spectroscopy and gas chromatography. Of these techniques, only gas chromatography is really useful at levels of organic matter present in seawater. With techniques available today such as glass capillary gas chromatography and mass spectrometry, much more information could be extracted from such samples [20]. 

Finally, the techniques of nmr, infrared spectroscopy, and thin-layer chromatography also can be used to assay maleic anhydride (172). The individual anhydrides may be analyzed by gas chromatography (173,174). The isomeric acids can be determined by polarography (175), thermal analysis (176), paper and thin-layer chromatographies (177), and nonaqueous titrations with an alkaU (178). Maleic and fumaric acids may be separated by both gel filtration (179) and ion-exchange techniques (180). 

Figures 2 through 9 are infrared spectra of fractions collected from partition columns, gas chromatography, thin-layer chromatography, or a combination of these separation techniques. Figure 10 is the infrared spectrum of a compound isolated by gas chromatography after hydrolysis of a pyrethrum concentrate. In this case the compound is a long-chain ester. All the infrared spectra were made with a Perkin-Elmer Model 221 instrument. The following operating parameters were used. A liquid demountable cell with a 0.01-mm path length was employed.

Qual and quan identification of expls is often fraught with difficulty owing to the inherent thermal instability of the compds which limits the use of vapor phase analytical techniques. If the expl is present in reasonably pure and coned form, infrared spectroscopy is suitable. Many times, especially if the expl is present in trace amts (mictogram quantities) ox if it is diluted with fillers (as in proplnts), separation and conen prior to identification are required. The earlier method, thin layer chromatography,... 

K. Wada, T. Tajima, and K. Ichimura, High sensitivity thin-layer chromatography—Fourier transform infrared spectrometry system based on zone transfer technique, Anal. Sci., 7 401 (1991). 

Chapter 14 discusses the very useful technique of thin layer chromatography. It has extensive applications in the analysis of complex mixtures of organic compounds and also has found limited applications in the analysis of organometallic compounds. No applications to anions and cations have been reported to date. The technique can also be used to prepare extracts suitable for subsequent examination by infrared spectroscopy or mass spectrometry. 

Several analytical techniques, such as infrared (IR) spectroscopy, differential scanning calorimetry, HPLC, and thin-layer chromatography (TLC), have been used to investigate possible drug degradation due to ultrasonic energy. No important permanent modification of the drug has been found, with the exception of the loss of crystallinity [89, 90],... 

This laboratory has examined the many techniques which are available. These range from the classic organic analytical methods of the 19th century through chemical spot tests, solution spectrophotometry, infrared, and other optical spectroscopic techniques through mass spectrometry. Thin-layer chromatography is, by itself, a separation technique which allows identification of the separated components by some appropriate technique. In many cases the patterns obtained may be sufiicient for identification, and in the hands of such workers as... 

GC- and LC-MS (Fig. 2), although others have also used other techniques including Fourier transform infrared spectroscopy, thin layer chromatography, high-pressure liquid chromatography, and Raman spectroscopy. The major techniques as judged by current number of publications will be discussed below. 

Note that Jenke " also cites references to the use of other related analytical techniques, including Head-space GC, high performance thin layer chromatography (HPTLC), supercritical fluid chromatography (SFC) /MS, and supercritical fluid chromatography/ Fourier transform infrared spectroscopy (SFC/FTIR). 

Thus, techniques used to give further evidence for the identity of a pesticide residue should be inteUigently chosen. If evidence from infrared or mass spectroscopy is not available, then adequate criteria of identification would be one or two GLC retention times, plus an Rp value from paper or thin-layer chromatography or an extraction p-value. Alternatively, one or two GLC retention times plus a GLC retention time of a derivative formed by chemical reaction would be a basis for confidence. 

Separation of mixtures of plasticisers can be achieved by thin layer chromatography on a Kieselgel plate using mixtures of benzene and ethyl acetate as solvents. The separated bands obtained can be examined by infrared techniques. 

The analytical technologies used In metabolomic investigations are nuclear magnetic resonance and mass spectrometry alone or in combination with liquid or gas chromatographic separation of metabolites (243). Other techniques include thin-layer chromatography, Fourier-transform infrared spectrometry, metabolite arrays, and Raman spectroscopy. 

We now have much better tools for assessing specificity than we had at the beginning of the pesticide age. Gas and thin layer chromatography can usually detect the presence of mixtures. They do not work so well the other way—proving the identity of a pure compound. For this you have to apply the instruments which work on the whole molecule, or appreciable or critical fractions of the molecule, such as infrared spectroscopy, nuclear magnetic resonance, or best of all, mass spectrometry. But there are always footnotes or reservations to the best of techniques. In this case, for unequivocal identification, apply the techniques only to pure samples only a small amount is needed, but it must be pure ... 

Analysis of amphetamines is commonly accomplished using a number of different methodologies. These include techniques such as thin-layer chromatography (TLC), gas chromatography (GC), liquid chromatography (LC), infrared spectroscopy, and mass spectrometry (MS). In addition, several different immvmoassays are commonly used for the analysis of amphetamines. 

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