Figure 1

Extracted negative ion chromatograms for the deprotonated organic acids [M - H]^-based on the theoretical mass-to-charge ratio used for detection and quantification. A standard mixture comprising all 24 organic acids was used. Therefore, extracted ion chromatograms show double peaks for the isobaric pair glucuronic/galacturonic acid and methylmalonic/succinic acid. For these pairs, glucuronic acid and methylmalonic acid eluted before their isobaric counterpart, respectively.