Sensitive simultaneous determination of 19 fluorobenzoic acids in saline waters by solid-phase extraction and liquid chromatography-tandem mass spectrometry.

A solid-phase extraction (SPE) procedure using C18 stationary phase was optimized for the preconcentration of 19 fluorinated derivatives of benzoic acid (FBA): mono-, di-, tri-, and tetrafluorosubstituted in the ring, trifluoromethylbenzoic acid and 3,5-bistrifluoromethyl benzoic acid from undiluted salt-rich (>20%) reservoir waters. Quantitative (>90%) retention/elution of 16 out of 19 analyte compounds was achieved allowing a fourfold preconcentration factor accompanied by the elimination of >99% of salt. For the three most polar compounds (2,6-dFBA, 2,3,6-tFBA, and 2,4,6-tFBA) the non-quantitative recoveries (>70%) were corrected by dedicated custom-synthesized deuterated internal standards. The FBAs were determined by HPLC - MS/MS revisited in terms of a choice of column, elution conditions and MS/MS signal acquisition parameters allowing the baseline separation and a gain in sensitivity. For a sample intake of 4 mL, detection limits for all the compounds in a reservoir water sample containing more than 20% salt were between 0.01 and 0.05 ng/mL which represents a gain of a factor of 10-20 in comparison with the state-of the art LC-MS/MS procedures for samples of similar complexity.