RESUMO
Per- and polyfluoroalkyl substances (PFAS), an emerging class of toxic anthropogenic chemicals persistent in the environment, are currently regulated at the low part-per-trillion level worldwide in drinking water. Quantification and screening of these compounds currently rely primarily on liquid chromatography hyphenated to mass spectrometry (LC-MS). The growing need for quicker and more robust analysis in routine monitoring has been, in many ways, spearheaded by the advent of direct ambient mass spectrometry (AMS) technologies. Direct analysis in real time (DART), a plasma-based ambient ionization technique that permits rapid automated analysis, effectively ionizes a broad range of compounds, including PFAS. This work evaluates the performance of DART-MS for the screening and quantification of PFAS of different chemical classes, employing a central composite design (CCD) to better understand the interactions of DART parameters on their ionization. Furthermore, in-source fragmentation of the model PFAS was investigated based on the DART parameters evaluated. Preconcentration of PFAS from water samples was achieved by solid phase microextraction (SPME), and extracts were analyzed using the optimized DART-MS conditions, which allowed obtaining linear dynamic ranges (LDRs) within 10 and 5000 ng/L and LOQs of 10, 25, and 50 ng/L for all analytes. Instrumental analysis was achieved in less than 20 s per sample.
RESUMO
The C-F alkyl structural backbone of per- and polyfluoroalkyl substances makes this class of molecules resistant to heat and degradation, leading to their high persistence and mobility in the environment and bioaccumulation in the tissues of living organisms. In this study, 15 PFAS with an alkyl chain length from C4 to C14, currently monitored by the U.S. Environmental Protection Agency (EPA), were preconcentrated by solid-phase microextraction (SPME) and analyzed by liquid chromatography-tandem mass spectrometry. The adsorption and desorption mechanisms of PFAS onto ion-exchange extraction phases was evaluated to understand the extraction process of PFAS from various environmental matrices under different conditions. This was achieved using two SPME geometries, namely fibers and thin films. The use of thin films resulted in a twofold improvement in extraction efficiency compared to fibers, especially for the short-chain PFAS. Methanol:water (80:20, v/v) was chosen as the optimized desorption solution, with ammonium formate added to minimize carryover. Extraction time profiles for both SPME geometries showed faster equilibration with thin films (30 min) compared to fibers (90-120 min). The linear dynamic range obtained with this method using fibers and thin films ranged from 10 to 5000 ng L-1 and 2.5-5000 ng L-1, respectively, with acceptable accuracy (70-130%) and precision (<15%). LOD ranged within 2.5-10 ng L-1 for fibers and 0.01-0.25 ng L-1 for thin films. Investigating the factors affecting PFAS recovery in complex samples enabled the quantitative assessment of PFAS contamination in various environmental water samples such as seawater, melted snow and biospecimens like human plasma. A 96-SPME holder was used for validation, which is compatible with sampling in 96-well plates and ensures high throughput in the analysis of real samples. The total concentration of PFAS detected in seawater and snow was 51.3 ng L-1 and 16.4 ng L-1, respectively.
RESUMO
Per- and polyfluoroalkyl substances (PFAS) are toxic and bioaccumulative compounds that are persistent in the environment due to their water and heat resistant properties. These compounds have been demonstrated to be ubiquitous in the environment, being found in water, soil, air and various biological matrices. The determination of PFAS at ultra-trace levels is thus critical to assess the extent of contamination in a particular matrix. In this work, solid phase microextraction (SPME) was evaluated as a pre-concentration technique to aid the quantitation of this class of pollutants below the EPA established advisory limits in drinking water at parts-per-trillion levels. Four model PFAS with varying physicochemical properties, namely hexafluoropropylene oxide dimer acid (GenX), perfluoro-1- butanesulfonate (PFBS), perfluoro-n-octanoic acid (PFOA) and perfluoro-1-octanesulfonate (PFOS) were studied as a proof of concept. Analysis was performed with the use of ultra-high pressure liquid chromatography-laminar flow tandem mass spectrometry (UHPLC-MS/MS). This study proposes the use of hydrophilic-lipophilic balance-weak anion-exchange/polyacrylonitrile (HLB-WAX/PAN) as a SPME coating, ideal for all model analytes. A sample volume of 1.5 mL was used for analysis, the optimized protocol including 20 min extraction, 20 min desorption and 6 min LC/MS analysis. This method achieved LOQs of 2.5 ng L- 1 (PFOS) and 1 ng L - 1 (GenX, PFBS and PFOA) with satisfactory precision and accuracy values evaluated over a period of 5 days.
