This also offers the additional new benefit of a nearly neutral pH extract which significantly reduces the risk of hydrolysis and acid-catalysed reactions. This is especially important for NTA, where the reactivity of unknown substances cannot be easily predicted. The selectivity of ammonium bicarbonate for SAX quaternary ammonium is intermediate between that of formate and chloride. Improved selectivity was evident from the full-scan acquisition total ion chromatograms (TICs, Figure ): by subtracting the total area of the TIC chromatogram generated by extracted ultrapure water from the average total area generated by samples (n=3), the proposed method returned 24% of the signal intensity generated by the WAX-based comparison method. Furthermore, the WAX-based comparison method resulted in significant amounts of brown precipitate absent from the method proposed here, which had to be removed by centrifugation. Overall, the method performance evaluation showed that the number of substances detected with the SAX-SPE method was consistently higher than that of the WAX-SPE method and regardless of the confidence level, with a total of 45 substances detected with SAX, versus 38 with WAX (n=3, see Figure ).