7-(Diethylamino)coumarin-3-carboxylic acid as derivatization reagent for 405 nm laser-induced fluorescence detection: A case study for the analysis of sulfonamides by capillary electrophoresis.

Diode lasers, especially 405 nm diode laser, as excitation sources offer new opportunities for laser-induced fluorescence (LIF) detection, but the lack of available derivatization reagents limits their widespread applications. Herein, a commercial fluorescent dye, 7-(diethylamino)coumarin-3-carboxylic acid (DEAC-C) was introduced as derivatization reagent and corresponding derivatization strategy for DEAC-C labeling sulfonamides was developed for 405 nm LIF detection. After systematic optimization, three sulfonamides including hydrochlorothiazide (HCTZ), chlorothiazide (CTZ) and chlortalidone (CTD) could be efficiently labeled by DEAC-C in the presence of cyanuric chloride and triethylamine (1.5%) in acetonitrile at 50 °C for 180 min. Based on the laboratory-built capillary electrophoresis-LIF system, a robust method was then proposed for the separation of DEAC-C labeled sulfonamides by micellar electrokinetic chromatography (MEKC) using the classic borax-SDS system. Under the optimized conditions, a baseline separation of three sulfonamides was achieved within 15 min, and the detection limits were determined to be 0.24, 0.29, and 0.23 nM for HCTZ, CTZ, and CTD, respectively. Furthermore, the developed MEKC-LIF method was validated using sulfonamide standards and spiked human urine sample and successfully applied for the analysis of three sulfonamides in complex pharmaceutical and physiological samples.