ISSN 1061-9348, Journal of Analytical Chemistry, 2011, Vol. 66, No. 5, pp. 476–481. © Pleiades Publishing, Ltd., 2011. 476 1 Fenoterol Hydrobromide (FNT), 1-(3,5-dihydrox- yphenyl)-2-(4-hydroxy-α-methylphenethylamino)etha- nol hydrobromide (Fig. 1a) is a direct-acting sympatho- mimetic with β-adrenoceptor stimulant activity largely selective for β 2 receptors. It is used as a bron- chodilator in the management of reversible airways obstruction [1]. B.P. [2] described an argentometric titration for determination of FNT in pure form. On the other side there is no official method for FNT in U.S.P. Several methods were described for the determination of FNT, both in pure form and in pharmaceutical prep- arations, these methods include spectrophotometry [3, 4], GC-MS [5, 6], HPLC [7, 8], voltammetry [9, 10] and capillary electrophoresis [11, 12]. Ritodrine hydrochloride (RTH), erythro-1-(p- hydroxyphenyl)-2-(4-hydroxyphenethylamino)propan- 1-ol hydrochloride (Fig. 1b) is a β 2 adrenergic agonist solely used as uterine relaxant. RTH is a direct-acting sympathomimetic agent with predominantly β-adren- ergic activity and selective action on β 2 -receptors. It decreases uterine contractility and is used to arrest premature labour and as an emergency means of alle- viating foetal asphyxia during labour [1]. B.P. [2] rec- ommended an HPLC method for its assay in the raw materials or pharmaceutical preparations. The litera- 1 The article is published in the original. ture contains several methods for determination of RTH in pharmaceutical dosage forms including; UV spectrophotometry [13], sequential injection spectrophotometry [14], colorimetry [15–18] and spectrofluorimetry [18]. DNS-Cl is one of the most widely used fluorescent probes, having versatile tolerance of conditions and broad range of functional group reactivity. DNS-Cl was used as labeling agent for a variety of phenolic ste- roidal estrogens [19, 20] and amphetamine [21]. Besides, DNS-Cl was used as labeling agent for deter- mination of propofol [22], anandamide [23], oxam- niquine [24], butylated hydroxyanisole [25], methyl paraben [26], promecarb [27], hydralazine [28], cloni- dine [29], and imidazoline derivatives [30]. The aim of the work is to develop a simple and sen- sitive spectrofluorimetric method for the determina- tion of FNT and RTH in bulk and in formulations after derivatization with dansyl chloride, EXPERIMENTAL Materials and reagents. All chemicals and solvents used were of analytical reagent grade. Ritodrine HCl reference standard was kindly provided by Solvay Duphar (the Netherlands). Pharmaceutical prepara- tions containing RTH include, Yutopar tablets (prod- Spectrofluorimetric Determination of Two β-Agonist Drugs in Bulk and Pharmaceutical Dosage Forms via Derivatization with Dansyl Chloride 1 M. E. Abd El-Ghaffar, D. R. El-Wasseef, D. T. El-Sherbiny, and S. M. El-Ashry Department of Medicinal Chemistry, Faculty of Pharmacy, University of Mansoura, Mansoura, 35516 Egypt Received October 29, 2009; in final form, September 30, 2010 Abstract—A sensitive, simple and rapid spectrofluorimetric method has been developed for the determina- tion of both Fenoterol hydrobromide (FNT) and Ritodrine hydrochloride (RTH) in pure and dosage forms. The method is based on derivatization using dansyl chloride (DNS-Cl) as fluorogenic agent and measuring the fluorescence of the products at emission wavelengths of 517 and 515 nm after excitation at 348 and 343 nm for FNT and RTH, respectively. Different experimental parameters affecting the fluorescence inten- sities were carefully studied and optimized. The relation between fluorescence intensities and drug concen- trations were rectilinear over the concentration range of 0.25–6.0 μg/mL for both drugs with a minimum detectability of 0.065 and 0.045 μg/mL for FNT and RTH, respectively. The percentage recoveries ±SD were 100.1 ± 0.9, 99.9 ± 0.6 for FNT and RTH respectively. The proposed method was successfully applied to the determination of both drugs in their commercial dosage forms. The obtained results were statistically vali- dated and agreed well with those obtained with reference methods. A suggestion for the reaction pathway with DNS-Cl was postulated. Keywords: Fenoterol hydrobromide, Ritodrine hydrochloride, spectrofluorimetry, dansyl chloride, dosage forms DOI: 10.1134/S1061934811050029 ARTICLES