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Utility of NBD-Cl as an electrophilic reagent for the determination of the two antihypertensive drugs hydrochlorothiazide and minoxidil in dosage forms and human urine samples

Heba Elmansi, Fathalla Belal, Mervat M.Hosny, and Omar M.EL-Abassy

Department of Pharmaceutical Analytical Chemistry, Faculty of Pharmacy, Mansoura University, Mansoura, Egypt



Received: 21 July 2020  Accepted: 27 November 2020


Sensitive and validated spectroscopic methods were developed for estimating the two antihypertensive drugs hydrochlorothiazide and minoxidil. The suggested methods relied on the reaction of each of the two drugs with 4-chloro-7-nitrobenzo-2-oxa-1 3-diazole (NBD-CL) as an electrophilic reagent and fluorescence derivatizing agent. Method (I) involves measuring the reaction products using spectrophotometry at 470 and 475 nm, for hydrochlorothiazide and minoxidil, respectively. The method covered the concentration ranges of 5.0–30.0 µg/ml and 1.0–10.0 µg/ml for hydrochlorothiazide and minoxidil, respectively. Method (II) is based on spectrofluorimetric measurement of the reaction products at 554 nm upon excitation at 470 nm and 475 nm for hydrochlorothiazide and minoxidil, respectively. The fluorescence-concentration plots were constructed through over 20.0–100.0 ng/ml for hydrochlorothiazide and 10.0–100.0 ng/ml for minoxidil. Successful determination of the studied drugs in dosage forms was accomplished with satisfactory percentage recoveries. Method II was further applied to the in-vitro determination of hydrochlorothiazide in human urine samples. It was found that the developed methods are economic and sensitive. The methods were validated by referring to the pharmacopeial guidelines. The reaction stoichiometry was assessed, and the mechanism was studied and explained.

Keywords: Hydrochlorotiazide; Minoxidil; NBD-CL; Urine; Dosage forms

Full paper is available at

DOI: 10.1007/s11696-020-01457-y


Chemical Papers 75 (5) 1925–1935 (2021)

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