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Reduction of LC/MS In-Source Fragmentation of HFPO-DA (GenX) Through Mobile Phase Additive Selection: Experiments to Increase [M-H]- Formation.
Citation:
Mullin, L., D. Katz, N. Riddell, R. Plumb, J. Burgess, AND I. Ericson Jogsten. Reduction of LC/MS In-Source Fragmentation of HFPO-DA (GenX) Through Mobile Phase Additive Selection: Experiments to Increase [M-H]- Formation. Society of Environmental Toxicology and Chemistry (SETAC) North America 39th Annual Meeting, Sacramento, CA, November 04 - 08, 2018.
Impact/Purpose:
Tetrafluoro-2-(heptafluoropropoxy)propanoic acid (HFPO-DA) is a replacement compound used to manufacture products such as Teflon®, because it is considered less persistent and less toxic than previously used per- and polyfluorinated alkanoic substances (PFAS). While this compound has previously been detected in the environment downstream of certain manufacturing facilities, little is known about the persistence, fate and toxicity of HFPO-DA. Existing methods for PFAS can be used to detect HFPO-DA, however present methods are not specifically designed to detect this compound. As a result, our ability to detect this compound is poor in comparison to other PFAS compounds. This work was undertaken to investigate methods to improve our ability to detect HFPO-DA. Our results describe the best conditions found for detecting and analyzing for HFPO-DA in the laboratory.
Description:
Tetrafluoro-2-(heptafluoropropoxy)propanoic acid (HFPO-DA), commonly known by the trade name GenX for the ammonium salt derivative, is a polyfluoroalkyl ether carboxylic acid introduced as replacement of perfluorinated alkanoic substances (PFAS) fomerly used in various industrial and consumer processes. Environmental monitoring of this compound has increased notably due to recently discovered prior high volume discharge by manufacturers. While liquid chromatography-tandem mass spectrometry (LC-MS/MS) using negative polarity electrospray ionization (ESI-) is the preferred method of analysis, fragmentation of the molecule upon ionization and dimer formation are common observations which inhibit low detection levels in environmental matrices and potential losses in analyte specificity. This work characterized the use of various LC mobile phase additives to control the formation of the bicarbonate adduct [M+CHO3]- of HFPO-DA. These included ammonium acetate, ammonium formate and ammonium bicarbonate (2 and 10mM); and formic acid and ammonium hydroxide (0.1 and 0.5%). All additive experiments were performed on a Waters Acquity H-Class equipped with an isolator column in line with pre-injection solvent delivery and a BEH C18 2.1x100 mm 1.7 m analytical column. Mass spectrometry analysis and source condition optimizations were performed on a Waters Xevo TQ-D operating in both full scan and MRM modes. Adduct identity was confirmed using accurate mass measurement on a Waters Xevo G2-XS QTof. Method reproducibility was assessed by repetition of optimized conditions on additional systems and sites. In monitoring the molecule stability across all mobile phases used, the previously characterized primary fragment generated from the loss of CO2 (-44Da) and additional fragments from breakage at either side of the ether linkage (-161 and -145Da) were assessed relative the parent molecule in full scan where minimal collision energy is applied. Formic acid mobile phase data showed the highest degree of molecule fragmentation. Adduct formation was most stable using the 2 mM ammonium bicarbonate and observed to reduce the degree of fragmentation contribution to overall molecular signal, as well as reduce dimer formation during ionization. An assessment of mobile phase pH from both multiple pH adjustments of ammonium bicarbonate and the inherent pH of all mobile phase compositions showed no strong correlation to in-source fragmentation increase, decrease or relative proportion to parent molecule conservation.