New method for quantification of ascorbic acid in fruit juices with an application of ionic liquids as phase modifier in reverse phase HPLC

Ascorbic acid (AA) is a major antioxidant in food and an indispensable vitamin for humans. Several analytical methods have been developed to track AA concentrations; however, only HPLC-based methods are selective enough to provide accurate concentration. The potential of the HPLC for AA quantification has been well-examined, yet ionic liquids (ILs) have not been tested for this purpose . ILs, when used as additives to mobile phases, have previously been shown to enhance chromatographic performance. In this study, the tetrabutylammonium methanesulfonate (TBA-MSA) was used as a phase modifier in reverse phase HPLC with fruit products serving as target matrices. Unexpectedly, increased TBA concentration lowers retention of ascorbate, contrary to established rules for ion-pairing reagents. It was found that the TBA is a effective stabilizer of AA in solution. The mechanism of retention was elucidated through the application of tetrabutylammonium chloride and methanesulfonate acid as phase additives. The AA content in fruit products by new HPLC and Tillman's titration techniques was found to be comparable. The method linearity range was 1.56 mg L −1 to 100 mg L −1 , with mean accuracy 100 % (97.1–103.6 %), and mean precision 0.7 (0.08–1.67 %). The accuracy of AA analysis in spiked samples was 107.0 % (95.2–122.0 %). This work presents not only the first IL application to AA quantification but also provides significant insights into behavior of the tetraalkylammonium cation in RP-HPLC. The developed method features straightforward sample preparation steps and can be applied the total vitamin C analysis in dark fruit juices. • First application of ionic liquid to test retention of ascorbate on reverse phase. • Tetrabutylammonium methanesulfonate (TBA-MSA) improves stability of ascorbic acid. • Mechanism of ascorbate retention driven by TBA is proposed. • Quantification of ascorbate show similar results by proposed and reference method. • New method is valuable for dark color juices.