A study of thin film solid phase microextraction methods for analysis of fluorinated benzoic acids in seawater

Abstract

Fluorinated benzoic acids (FBAs) are frequently used as tracers by the oil industry to characterize petroleum reservoirs. The demand for fast, reliable, robust, and sensitive approaches to separate and quantify FBAs in produced water, both in laboratory and field conditions, has not been yet fully satisfied. In this study, for the first time, thin film solid phase microextraction (TF-SPME) is proposed as a versatile sample preparation tool for the determination of FBAs in produced water by pursing two different approaches. First, an automated high throughput TF-SPME method using solvent desorption for fast and simultaneous preparation of multiple samples prior to liquid chromatographic separation and high resolution mass spectrometric detection (LC–MS) of FBAs was demonstrated for routine laboratory analysis. This method was optimized in terms of extraction phase chemistry, sample pH and ionic strength, extraction/desorption times using two representative FBAs (4-FBA and 2,3,4,5-tetra FBA). It incorporates a relatively simple sample pretreatment involving pH adjustment prior to the TF-SPME, and obtained limits of quantification (LOQ) are at the 1.0ngmL−1 level. Second, the applicability of TF-SPME for fast mass spectrometric (MS) determination of FBAs with omission of derivatization and gas chromatographic (GC) separation was proven. This second method consists of manual extractions of analytes from seawater samples with a thermally stable TF-SPME membrane and direct thermal desorption of the extracted FBAs to a MS via a thermal desorption unit (TDU). It was demonstrated that the TF-SPME extracts and thermally releases analytes quantitatively and with good reproducibility. This approach opens up the possibility for on-site measurements with portable analyzers.