Simultaneous determination of nine related substances in p-phthalic acid residue by RP-HPLC

A high-performance liquid chromatography with ultraviolet detection (HPLC-UV) is established for the simultaneous determination of p-phthalic acid, benzoic acid, 4-carboxybenzaldehyde, m-phthalic acid, o-phthalic acid, phthalide, o-toluic acid, m-toluic acid and p-toluic acid in the residue generated during the production of p-phthalic acid (PPA). On a narrow-diameter reversed-phase C18 column, gradient elution is applied with a methanol-water-ammonium acetate-acetic acid buffer (100 mmol/L, pH 4.70) as mobile phase at a flow rate of 0.2 mL/min, and detection is operated by UV absorption at a wavelength of 254 nm. Under the conditions, these nine relative compounds, including organic acids, are well separated. The detection limits (S/N = 3) are 0.05 µg/mL-0.20 µg/mL, and the correlation coefficients of standard curves are between 0.99995 and 0.99999. Relative standard deviations for analyses of real samples are below 5.3%, and recoveries of these determined compounds ranges from 90.0 to 104.9%. The method, which provides accurate and reliable results, can effectively guide the recycling and reutilization of organic acids and related substances in PPA residue.