Original article Cinchocaine hydrochloride determination by atomic absorption spectrometry and spectrophotometry Nour T. Abdel-Ghani, Ahmed F.A.Youssef *, Mohamed A. Awady Chemistry Department, Faculty of Science, Cairo University, Giza, Egypt Received 15 September 2004; received in revised form 28 February 2005; accepted 8 March 2005 Available online 28 April 2005 Abstract Two sensitive spectrophotometric and atomic absorption spectrometric procedures have been developed for determination of cinchocaine hydrochloride (Cin.Cl) in pure form and in pharmaceutical formulation. The spectrophotometric method was based on formation of an insoluble colored ion-associate between the cited drug and tetrathiocyanatocobaltate (CoTC) or hexathiocyanatochromate (CrTC) which dissolved and extracted in an organic solvent. The optimal experimental conditions for quantitative extraction such as pH, concentration of the reagents and solvent were studied. Toluene and iso-butyl alcohol proved to be the most suitable solvents for quantitative extraction of Cin- CoTC and Cin-CrTC ion-associates with maximum absorbance at 620 and 555 nm, respectively. The optimum concentration ranges, molar absorptivities, Ringbom ranges and Sandell sensitivities were also evaluated. The atomic absorption spectrometric method is based on measuring of the excess cobalt or chromium in the aqueous solution, after precipitation of the drug, at 240.7 and 357.9 nm, respectively. Linear application ranges, characteristic masses and detection limits were 57.99–361.9, 50.40 and 4.22 μg ml –1 of Cin.Cl, in case of CoTC, while 37.99–379.9, 18.94 and 0.81 μg ml –1 in case of CrTC. © 2005 Elsevier SAS. All rights reserved. Keywords: Cinchocaine hydrochloride (dibucaine); Ion associates; Spectrophotometry; Atomic absorption spectrometry; Ointment analysis 1. Introduction Cinchocaine hydrochloride [61-12-1] (dibucaine) [2-butoxy-N-(2-diethylaminoethyl) quinoline-4-carbox- amide hydrochloride] is a drug that was first synthesized by Miescher [1]. This compound has attracted a great clinical interest as a local anesthetic. It is about 15 times more potent than procaine and five times more potent than cocaine in pro- ducing local anesthetic, but it is also considerably more poi- sonous [2]. Cinchocaine is commonly employed as a free base or as hydrochloride in ophthalmic ointments to produce con- junctival anesthesia or in dilute penetrable solutions to pro- duce spinal or surface anesthesia. Cin.Cl under investigation is represented by the following formula, where Bu n : n-butyl and Et: ethyl. Cinchocaine hydrochloride. Several procedures have been reported in the literature for the analysis of cinchocaine HCl (Cin.Cl). These methods are spectrophotometry [3–7], fluorimetry [8], high performance liquid chromatography (HPLC) [9], gas chromatography (GC) [10,11], thin-layer chromatography [12], electrophoresis [13], polarography [14], ion-selective electrodes [15,16] and titri- metry [17,18]. British pharmacopoeia specified potentiomet- ric titration for the determination of Cin.Cl [19]. On the other hand, metal ions such as Cr(VI) and Co(III) are widely used as precipitating agents for analysis of many pharmaceutical compounds [20,21]. However, there is no lit- erature data about their usage as ion-associates forming reagents with the studied drug. * Corresponding author. Fax: +20 2 568 5799/572 8843. E-mail address: afay68@hotmail.com (A.F.A.Youssef). Il Farmaco 60 (2005) 419–424 http://france.elsevier.com/direct/FARMAC/ 0014-827X/$ - see front matter © 2005 Elsevier SAS. All rights reserved. doi:10.1016/j.farmac.2005.03.001