Talanta 64 (2004) 1226–1232 Flow-injection determination of phenylephrine hydrochloride in pharmaceutical dosage forms with on-line solid-phase extraction and spectrophotometric detection  Moisés Knochen ∗ , Javier Giglio Universidad de la República, Facultad de Qu´ ımica, Departamento “Estrella Campos”, Av. Gral. Flores 2124. Casilla de Correo 1157, 11800 Montevideo, Uruguay Received 3 March 2004; received in revised form 30 March 2004; accepted 30 March 2004 Available online 11 September 2004 Abstract A flow injection method is proposed for the determination of phenylephrine hydrochloride in pharmaceutical dosage forms. The method involves the use of on-line solid-phase extraction by means of a microcolumn containing Dowex 50W X8 ion-exchange resin for the separation of the analyte prior to colour development and spectrophotometric detection in the visible region. The influence of preconcentration flow, preconcentration pH and elution volume was studied. The method exhibits appropriate linearity (r 2 = 0.9999) which was proved statistically by means of the “F”-test. When applied to commercial samples containing several active ingredients and excipients, a significant reduction of interferences was found. Accuracy, evaluated by means of the spike recovery method was in the range 99.7–100.8%, with precision (R.S.D., %) better than 1%. In order to achieve the automation the system was controlled from a notebook computer by means of a program written in QuickBASIC language. Under these conditions, a sampling frequency of 40 samples per hour could be attained. © 2004 Elsevier B.V. All rights reserved. Keywords: Flow injection; Pharmaceutical; Phenylephrine; Solid phase extraction; Spectrophotometric detection 1. Introduction Phenylephrine hydrochloride ((R)-3-hydroxy--[(methyl- amino)methyl] benzenemethanol hydrochloride) is a sym- pathomimetic drug used for nasal congestion, sinusitis and rhinitis. It is also used in ophthalmology as a mydriatic and conjunctival decongestant [1]. It is incorporated in a num- ber of pharmaceutical preparations either alone or, more frequently, associated with other active ingredients. Dosage forms include tablets, syrups, eye drops and injections. Among the methods currently established for the deter- mination of this substance, one of the most frequently used is high performance liquid chromatography (HPLC), for in- stance in the United States Pharmacopeia (USP) for the de-  Presented in the 12th International Conference on Flow Injection Analysis and Related Techniques (12th ICFIA), M´ erida, Venezuela, December 7–13, 2003. ∗ Corresponding author. Tel.: +598 2 9241808; fax: +598 2 9241906. E-mail address: mknochen@fq.edu.uy (M. Knochen). termination in pharmaceutical dosage forms (Phenylephrine Hydrochloride Injection, Nasal Jelly and Ophtalmic Solu- tion) [2]. The same is true for the British Pharmacopoeia [3] in the Phenylephrine Eye Drops monograph. Direct spectrophotometric measurements can be carried out only in the absence of other UV-absorbing substances. An example of this is the Phenylephrine Injection mono- graph in the British Pharmacopoeia. Visible spectrophotom- etry [4] and chemiluminescence [5] have also been pro- posed. Unfortunately, chromogenic or luminogenic reactions may be interfered by excipients or other active ingredients co-formulated in the dosage form. The literature is scarce in methods for the determination of phenylephrine in more complex dosage forms, consist- ing of several active substances or more complicated ve- hicles, which are often found in oral solutions. Spectroflu- orimetry has been proposed for this purpose [6,7]. HPLC is also a good technique for resolving complex mixtures, however, the investment and operating costs are high. For some purposes, the high investment may not be justified. 0039-9140/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.talanta.2004.03.071