RESUMO
Alkanes, cycloalkanes and arenes have rather different sensitivities to IR-spectrometric determination, leading to high relative uncertainty (δc) for the total petroleum hydrocarbon index (TPH) in natural and waste waters. Another source of TPH uncertainty is the mismatch of group composition of the hydrocarbon mixture in the sample and in the standard substance used for one-dimensional calibration. Increasing the number of wavelengths and using of multivariate calibrations permit the reduction of δc to <10% rel. These calibrations may be constructed from IR-spectra and findings of extracts from aqueous solutions with known content of hydrocarbons. The method takes into account the losses of hydrocarbons during sample preparation. The accuracy of TPH estimations for this method is much better than for standard methods based on one-dimensional calibration with Simard mixture. This new method is useful in produced waste water analysis.
RESUMO
The estimation of sum content of similar analytes without their separation often requires the use of total indices (TIs) expressed in terms of the standard substance concentration. Theoretic and metrological features of such indices are discussed in the review. The sum content of similar analytes is estimated by any TI with a certain systematic error. It can be minimized by selecting a standard substance and/or with the justification of sensitivity coefficients for individual analytes. The publications are pointed out in which new TIs are offered or new methods to measure known TIs are described. The corresponding studies are predominantly associated with two kinds of estimates: (a) total content of organic substances in waters and (b) the total antioxidant activity of foodstuffs.
