Chromatographic fingerprints of industrial toluic acids established for their quality control

The chromatographic fingerprints of industrial o-toluic acid, m-toluic acid and p-toluic acid have been established by HPLC-UV detection according to their impurity groups. HPLC separation of all relative substances involved in the groups was developed on a Kromasil C18 column by using methanol–water–NH4Ac-HAc buffer (100 mM, pH 4.70) 15/65/20 (v/v/v) as the mobile phase at a flow rate of 1.5 mL/min, and detection was operated by UV adsorption at a wavelength of 254 nm. The ultraviolet spectra corresponding to each chromatographic peak were also recorded for further identification of all components. Whether the limits of relative impurities residues in a toluic acid product are qualified or not can be intuitively estimated by analyzing its chromatogram with comparison to the fingerprint. This protocol has successfully provided some Chinese manufacturers with a simple and feasible method for quality control of toluic acids for industrial use.