Confidence was further enhanced as a washing step could be included during SPE, which likely further enhanced anion selectivity through elimination of weak hydrogen bonding or dipole interactions with the silica polymer backbone. Such washing steps are generally not included in any other NTA sample preparation approaches to our knowledge. Research into other relevant substances revealed 4-chloro-2-methylphenolate to be an in-source fragmentation product of 2-methyl-4-chlorophenoxyacetic acid (MCPA), a well-known acidic herbicide. The extracted ion chromatogram of the [M-H] -of both herbicides showed matching peaks. The identity was further confirmed by injection of a reference material. An erroneous identification was consequently averted using this approach.