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Organic Chemistry and Compound Detection
COMPOUND DETECTION in organic chemistry refers to the methods of separation and identification of organic compounds. In modern technology this involves the use of chromatography (paper, thin-layer, gas–liquid, high-pressure liquid); spectroscopy (infrared, Raman ultraviolet and visible, nuclear magnetic resonance); mass spectrometry; and reaction chromatography (chemical reactions on thin-layer plates or gas chromatographic columns which can be carried out prior to, during, or immediately after the chromatographic separation). Pyrolysis and X-ray crystallography of organic compounds furnish important structural information on the partial structures or on the whole molecule, respectively. The combination (and computerization) of chemical, chromatographic, and spectroscopic techniques has become a more efficient tool for the detection and identification of organic compounds than any of these techniques.
It was only about 40 years ago that chemists had the tedious task of identifying and characterizing unknown organic compounds especially in the area of natural products. This may involve degradation of the molecule followed by synthesis involving many steps. For example Woodward elucidated the structure of strychnine in 1947 and seven-years later successfully synthesized this compound.
The advent of computers and Fourier transform completely revolutionized the detection and identification of organic compounds. Modern automated instruments allow very small samples in the nanogram (10−9 g) range to be characterized in a very short time. The application of Fourier transform nuclear magnetic resonance (FTNMR) and Fourier transform infrared (FTIR) allows recovery of the sample in contrast to mass spectrometric (MS) determination which is a destructive but quite often necessary technique.
Modern methods especially in the separation of complex organic mixtures utilizing gas–liquid chromatography (GLC), high-pressure liquid chromatography (HPLC), and droplet counter-current (DCC) chromatography can separate samples rapidly and efficiently in the picogram range which until fairly recently has been impossible. Coupling the chromatographic instruments to spectrometers enables a partially automated analysis in even less time. The following coupling of chromatographic instruments has been performed: GC–MS, GC–FTIR, GC–MI–FTIR, GC–UV–VIS, HPLC–MS, HPLC–FTIR, HPLC–FTNMR and MS–MS. (Fig. 1).
These semi-automated systems of analyzing and characterizing small samples are vital to the natural product organic chemist and biochemist for detection of highly active substances in extremely low concentration in living organisms. A typical example is in the field of pheromones which includes insect sex attractants which differ quite markedly in many insects. The concentration has often been found in the 10−9–10−12 g range.
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