Organic substances, determination

Paschke, A., Popp, P., Schuurmann, G. (1999) Water solubility and octanol/water-partitioning of hydrophobic chlorinated organic substances, determined by using SPME/GC. Fresenius J. Anal. Chem. 360, 52-57. 

Ammonia may be estimated by dissolving the gas in a known volume of standard acid and then back-titrating the excess acid. In a method widely used for the determination of basic nitrogen in organic substances (the Kjeldahl method), the nitrogenous material is converted into ammonium sulphate by heating with concentrated sulphuric acid. The ammonia is then driven off by the action of alkali and absorbed in standard acid. 

J. L. Graham, W. A. Rubey, and B. Dellinger, "Determination of Thermal Decomposition Properties of Toxic Organic Substances," Summer National Meeting AlChE, Cleveland, Ohio, Aug. 1982. 

IR SPECTROMETRICAL DETERMINATION OF VOLATILE ORGANIC SUBSTANCES IN WATERS AFTER EXTRACTION INTO GASEOUS PHASE... 

Where M is the molecular weight of the solute, Dt is the elevation of boiling point in °C, c is the concentration of solute in grams for lOOOgm of solvent, and K is the Ebullioscopic Constant (molecular elevation of the boiling point) for the solvent. K is a fixed property (constant) for the particular solvent. This has been very useful for the determination of the molecular weights of organic substances in solution. 

The shape of the equilibrium line, or solubility curve, is important in determining the mode of crystallization to be employed in order to crystallize a particular substance. If the curve is steep, i.e. the substance exhibits a strong temperature dependence of solubility (e.g. many salts and organic substances), then a cooling crystallization might be suitable. But if the metastable zone is wide (e.g. sucrose solutions), addition of seed crystal might be necessary. This can be desirable, particularly if a uniformly sized product is required. If on the other hand, the equilibrium line is relatively flat (e.g. for aqueous common salt... 

Even before a new organic substance has its structure determined, it must be purified by separating it from solvents and all contaminants. Purification was an enormously time-consuming, hit-or-miss proposition in the 19th and early 20th centuries, but powerful instruments developed in the last few decades now simplify the problem. 

Standards are available which cater for the performance of over 400 chemical analyses these include the determination of several metals and of a number of organic substances, including many of biochemical significance. 

The more advanced spectrofluorimeters are capable of automatically scanning fluorescent spectra between about 200 and 900 nm and produce a chart record of the spectrum obtained. These can also operate at a fixed wavelength and are equally suitable for carrying out quantitative work their main application tends to be for the detection and determination of small concentrations of organic substances. 

Almost all of the methods described in Chapter 23 can be used for in vivo analyses, both voltammetric and potentiometric ones. The former are used primarily in the analysis of organic substances, which, within certain ranges of potential, can be either oxidized or reduced. Another popular method is the amperometric determination of oxygen in different biological media with the Clark electrode (Section 23.3). 

It is an important role plaid by singlet oxygen in oxidizing organic substances that does determine the interest in the study of interaction between 02( A ) and the surface of these substances. Application of... 

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