A novel pre-column fluorescent derivatization method for the sensitive determination of aristolochic acids in medicinal herbs by high-performance liquid chromatography with fluorescence detection

Aristolochic acids (AAs) are a family of structurally related nitrophenanthrene carboxylic acids existing in Aristolochia, Bragantia, and Asarum species. AAs have been proven to have nephrotoxic and carcinogenic toxicity. In this study, a novel pre-column fluorescence derivatization procedure followed by high-performance liquid chromatography-fluorescence detection (HPLC-FLD) is developed for the analysis of AAs in medicinal herbs. The nitro group in the phenanthrene ring of AAs was removed by NaBH₄ in water–THF (2:1, v/v), resulting in the corresponding aristolic acids. The analysis of AAs in medicinal herbs was based of the sensitive fluorescence detection of aristolic acids after the chemical derivatization. Because the produced aristolic acids are highly fluorescent the limit of detection (LOD) of AAI and AAII were lowered to 0.06 and 0.04 ng/mL, respectively, which is at least an order of magnitude lower than those in the reported HPLC and LC–MS methods. Good linearity with correlation coefficients higher than 0.997 were obtained for AAI and AII in the calibration ranges of 0.2–800 ng/mL. The derivatization conditions such as reaction temperature, time and the amount of NaBH₄ were optimized. The developed method provided satisfactory intra-day and inter-day precisions with RSDs less than 1.4% and 3.8%, respectively. The relative analytical error was less than 7% for the analysis of AAI and AAII in spiked matrix samples.