High-Performance Liquid Chromatography Using Ultraviolet Detection for Separation of Terephthalic Acid and Associated Impurities from Recycled Materials

An optimized rapid and precise high-performance liquid chromatography method has been developed to separate, identify and quantitate impurities contained within terephthalic acid (TPA) produced from recycled materials. Using a Waters X-Select HSS T3 column for the separation of recycled TPA and eight impurities, and a mobile phase of H2O/CH3CN containing 0.1% trifluoroacetic acid (TFA) with detection by UV at 250 nm, baseline separation of all compounds was achieved in ˂17 min. Four different mobile phase acidic additives were tested, the results indicating that mobile phases with lower pH provided better separation of the compounds with accompanying improved peak shapes. Among all the acidic additives tested in this study, a mobile phase containing 0.1% TFA demonstrated the highest resolution and the best peak shapes. It was concluded that by suppressing the ionization of the acidic compounds contained in the samples through increased acidity of the mobile phase, better peak shapes and higher resolution could be achieved. The amount of increased mobile phase acidity was based in part on the pKa values of the analytes and adjusted so as to eliminate as much as possible any dissociation of the organic acids. A comparison of a standard addition method versus an external calibration curve approach for the quantification of impurities showed similar results, even for relatively low-concentration analytes at levels below 10 ppm. The aspects often linked with validated analytical methods were addressed including linearity, limit of detection, limit of quantitation, sensitivity and selectivity, addressing the criteria set forth in the acronyms of the QuECHERS method description, that is quick easy, cheap, effective, rugged and safe.