Protocols for Measurement of Naphthenic Acids in Aqueous Samples

Abstract

Naphthenic acids (NAs), a group of polar organic carboxylic acids that naturally occur in crude oil, have been of concern since the turn of the twentieth century due to corrosion of petroleum refineries. In the last two decades, naphthenic acids have been a focus of concern in the Canadian oil sands since they were identified as the main cause of acute toxicity of the wastewater stream following ore processing. Numerous analytical techniques are employed for NA measurement. A universally accepted method has yet to be developed. Additionally, all techniques are semiquantitative as appropriate standards for calibration do not exist. Properties such as toxicity, biodegradability, and susceptibility to other treatment regimes depend on NA structure; measurement of total NA concentration is insufficient when examining these properties in detail. The use of high-resolution methods reduces errors to which low-resolution techniques are prone, but are expensive and difficult to access. The protocols chosen for inclusion here are more widely accessible and sufficient for most applications. Total acid number and Fourier transform infrared spectroscopy are used to estimate acid content and acid-extractable organic content, respectively. Gas chromatography will specifically target NAs, and coupled with mass spectrometry, the characterization of an NA mixture is possible. However, while low-resolution gas chromatography–mass spectrometry is widely available and recommended for most uses, awareness that this technique is prone to misclassification and false positive data is essential.