Organic compounds determination, rapid methods

Infrared Spectrophotometry. The isotope effect on the vibrational spectmm of D2O makes infrared spectrophotometry the method of choice for deuterium analysis. It is as rapid as mass spectrometry, does not suffer from memory effects, and requites less expensive laboratory equipment. Measurement at either the O—H fundamental vibration at 2.94 p.m (O—H) or 3.82 p.m (O—D) can be used. This method is equally appticable to low concentrations of D2O in H2O, or the reverse (86,87). Absorption in the near infrared can also be used (88,89) and this procedure is particularly useful (see Infrared and raman spectroscopy Spectroscopy). The D/H ratio in the nonexchangeable positions in organic compounds can be determined by a combination of exchange and spectrophotometric methods (90). 

Brooker, P.J. and Ellison, M. The determination of the water solubility of organic compounds by a rapid turbidimetric method, Chem. Ind., (October 1974), pp. 785-787. 

A rapid and relatively simple method was applied to determine the toxicity of water by using the concentration procedure prior to testing with the Ames test (15). The organic compounds were isolated, after filtering the water, on a mixture of XAD-4.XAD-8 (1 1). The acetone in the XAD eluate was removed by a stream of purified nitrogen. 

Tuckerman and collaborators state that chloric acid is to be preferred to the more widely used sulphuric acid or sulphuric-nitric acid digestions or alkaline fusions recommended for the determination of arsenic in organic compounds. Excess chloric acid is easily removed by boiling to leave a perchloric acid solution of inorganic As(V). Rapid micro and semi-micro methods for the determination of arsenic based on chloric acid digestion are described. 

In clinical chemistry the determination of stable elements by radiochemical methods offers no outstanding advantages over alternative methods, but the use of radioisotopes for determining organic compounds is developing rapidly. In isotope dilution methods (G6), a pure but radioactive form of the compound to be measured is mixed with the sample, a fraction is isolated, and its activity is determined. In radio-metric or derivative analysis (W14), a radioactive reagent is allowed to react with the analyte the labeled compound is separated and its activity is measured. The isotopes commonly used are C,... 

The heat evolved on combustion, i.e. on the complete oxidation of combustible substances, is of particular interest. From the heat of combustion of an organic compound we can calculate its heat of formation. This quantity is of considerable importance, but cannot be measured directly, as the preparation of organic compounds from the elements is either impossible, or only possible under conditions which cannot be reproduced inside a calorimeter. It is necessary to emphasise the fact that only very rapid reactions can be treated calorimetrically, for the interchange of heat with the surroundings during a slow reaction becomes so great that even approximate measurements are impossible. As most organic reactions are very slow, we are forced to determine the heat of reaction by an indirect method, viz. from the determination of the heat of combustion. 

This automatic classification is based on the value of the coefficient contribution of the reference spectra used in the semi-deterministic method (see Chapter 2). The reference spectra are related to suspended solids, colloids, dissolved organic compounds, surfactants and nitrate. For the determination of the coefficient values, an important experiment has been carried out [17], The deconvolution procedure was applied, on one hand, to several raw or treated samples taken at the inlet and outlet of several hundreds of waste-water treatment plants of different types, and, on the other hand, to a lot of surface water samples polluted with treated wastewater discharges. Table 5 shows the coefficients of the reference spectra for some of these samples (the coefficient values correspond to samples without dilution). The interpretation of the coefficients can lead to a rapid characterisation of the effluent type (inlet or outlet) and of the treatment plant type (chemical, biological, etc.). 

In a promising development of oxygen determination, Kirsten [106] carried out the pyrolytic determination of oxygen in organic compounds at 1020°C with the use of amorphous carbon containing 20% of nickel. An important feature of the method is the addition of chlorohydrocarbon vapour to the flow of carrier gas. Kirsten [106] found that the reactor, i.e., the quartz tube, is rapidly rendered inoperative if the temperature is increased above 1020°C. To obtain quantitative results, it is sufficient to evaporate 1-chloropentane at a rate of 18ql/h. At present the Kirsten method is applied to Carlo Erba instrumentation. 

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