In this application note we explore the use of high resolution mass spectrometry, with high efficiency ion mobility-based measurements and separations as an important tool for the unequivocal identification of PFOS isomers in environmental samples. Ion mobility spectrometry (IMS) is a rapid, orthogonal, gas phase separation technique which allows another dimension of separation to be obtained within an LC timeframe. Compounds can be differentiated based on size, shape, and charge. In addition, both precursor ion and fragment ion information can be acquired in a single injection for all components analyzed.