The estimation of total petroleum hydrocarbons content in waste water by IR spectrometry with multivariate calibrations

• One-wave IR spectrometric determination of TPH produces too large uncertainty (>50 %)
• Using of multiwave and multivariate calibrations diminishes this uncertainty to 6-8 %
• Various aqueous solutions with known TPH were used to construct required calibrations.
• New method for TPH determination does not demand the standard substance selection.
• The method was tested in waste water analysis and approved for TPH > 0.5 mg/dm3

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.

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