The importance an increased method selectivity for acids for high-quality structural elucidation was experienced multiple times whilst processing SS results. Figure compares the number of substances detected in the same sample with the proposed method and with WAX (n=3), totalling respectively 45 and 38. Only one substance was detected exclusively with the comparison method (2-bromo-4-nitrophenol, at Level 4). The extracted ion chromatogram and spectra of 2,2,4-tribromo-5-hydroxycyclopent-4-ene-1,3-dione, dibromomethanesulfonic acid, and 6:2 FTSA (6:2 fluorotelomer sulfonic acid) in a London tap water sample are shown in Figure as examples of the quality of data generated by this method. An example of how selective extraction could facilitate qualitative analysis was in the case of a peak detected in one sample and returning library matches for three isomers of monochloro-cresols (with a measured [M-H] -m/z of 141.0110 and a matching elemental composition of C7H6ClO -). However, these structures are not expected to be acidic and consequently are not expected to be retained by this silica-based SAX-SPE method.