Figure 2.

Retention time (RT) and response curve characterization of seven compounds with C₇H₇NO₂ formula in positive ionization mode on zic-HILIC chromatography. Peaks of the characterized compounds are indicated by black arrows. The elution order of the methyl-nicotinic acid and aminobenzoates (A–D) was confirmed by the constant RTs of the tIS (technical internal standards). The analytical standard of 2-pyridylacetic acid (E) shows two peaks at 4.6 and 5.9 min, the later having the same RT as 3-pyridylacetic acid (see Figure S1) (F). Trigonelline (G) is detected at lower amounts than other compounds with the same formula. The shown MS2 spectra were deconvoluted using MS2Dec from the injection, indicated by a blue dot in the response curve.