Determination of benvitimod in cosmetics by HPLC with pre-column fluorescence derivatization using 2-((7-nitrobenzo[c][1,2,5]oxadiazol-4-yl)oxy)benzoic acid (NBD-SA).

Benvitimod is a non-steroidal tyrosine protein kinase inhibitor commonly used to treat psoriasis. However, it can cause adverse reactions such as contact dermatitis and itching, which can seriously impact consumer health. This study involved designing and synthesising a novel fluorescent labeling reagent, 2-((7-nitrobenzo[c][1,2,5]oxadiazol-4-yl)oxy)benzoic acid (NBD-SA). This reagent is used to detect benvidimod in cosmetics using high-performance liquid chromatography with fluorescence. With the help of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride/4-dimethylaminopyridine catalysts, NBD-SA can react at 45 °C within an hour, thus providing a quick and effective labeling method for benvitimod. The resulting derivative exhibits remarkable stability and fluorescence properties. The maximum excitation wavelength is 461.96 nm, and the emission wavelength is 578.97 nm. Four cosmetic formulations were completely separated by using a CAPCELL PAK C18 column and gradient elution. Under the optimum conditions, the standard curve shows a good linearity with a determination coefficient of r2 = 0.9999. The LOD and LOQ were 0.04 ng mL-1 and 0.11 ng mL-1, respectively. Thus, NBD-SA was successfully used to detect benvitimod that had been illegally added to cosmetics.