There has been an increasing awareness of the presence of polyfluorinated alkyl substances (PFAS) in water. A simple and robust method with quick turn-around time to determine these compounds is essential to providing accurate responses in a timely manner. In the method presented here, direct injection without solid-phase extraction (SPE) allows us to maximize throughput and to minimize background caused by the sample preparation step. We used liquid chromatography with triple-quadrupole mass spectrometry (LC–MS/MS) to analyze the fluorotelomer and unsaturated fluorotelomer
acids included in ASTM International method 7968/7979. Fluorotelomer acids are observed as [M-H]- and [M-HF-H]-. Since the loss of HF in the fluorotelomer acids results in an ion with the same formula as the unsaturated fluorotelomer acids, and these two classes of compounds showed very similar retention times, we reduced the electrospray ionization (ESI) heater temperature to reduce HF loss and minimize false identifications.