Profiling organic acids in produced water samples using vacuum-assisted sorbent extraction and gas chromatography coupled to Fourier transform Orbitrap mass spectrometry

Abstract

In this article, we describe the preliminary findings obtained with headspace vacuum-assisted sorbent extraction (VASE) as an alternative for sample preparation in the analysis of organic acids in produced water (PW). VASE is a headspace technique that combines the use of high-capacity sorbent traps and low-pressure conditions. Method development included extraction parameters and thermal desorption conditions. Multivariate optimization using design of experiments (DOE) was performed for variable screening and method optimization. A microwave-assisted derivatization protocol was proposed to convert the organic acids into its corresponding methyl esters (ME). The reaction was conducted in-sample prior to VASE extraction, and had the advantage of dismissing the use of organic solvents. The isolated fraction was analyzed by gas chromatography coupled to high resolution mass spectrometry (GC-HRMS). Quantitative analysis exhibited a linear range from 1 to 100 µg L-1. The reported detection limits ranged from 0.001 to 0.070 µg L-1 using the model acids. The method was successfully applied for qualitative analysis of PW samples. It was possible to detect important classes, such as hydrocarbons, oxygen- and nitrogen- containing compounds. Several NAs species with different double-bond equivalent (DBE) values and carbon numbers could be found in both samples. The greenness of the analytical method was also evaluated, exhibiting better environmental metrics when compared with traditional liquid–liquid extraction.