This paper describes the formation of a self-assembled monolayer of 11-mercaptoundecanoic acid (MUA) under different concentrations on a gold sensor disk, monitoring in situ and in real time using surface plasmon resonance spectroscopy (SPR). The film thickness and dielectric constant were determined for a fully formed monolayer using one-color approach SPR. The kinetic studies of the film formation in ethanol solution indicated that the self-assembled monolayer is formed in a two-step adsorption process. In this sense, this unpublished route was applied on the basis of a model where many molecules are adsorbed at an initial step and then can be desorbed and/or rearranged to form a perfect monolayer.

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1IntroductionThem ost used methods for the determination of drugsi n pharmaceutical samples are basedo nh igh performance liquid chromatography (HPLC) using an UV detector. Despite of these methods being highly robust, in general they present some drawbacks such as high generation of waste and low analyticalf requencyf or routine analysis. Thee lectroanalytical techniques have shown to be an attractive alternativeness for the determination of drugs in pharmaceutical formulations.T he electroanalytical methods present high selectivity because most of active components in formulations are electroactive species while the excipients do not present any faradaic response.F urthermore,t he electrochemical detection providesh igh sensitivity,l ow-cost and fast analysis with less waste generation. Ar ecentr eview of Uslu and Ozkan has listed more than 200 pharmaceutical compounds that were determined by electrochemical detection [1].A notheri mportanta dvantage of electroanalytical methodsi st he possibility of simultaneous determinations of two or more associateda ctive ingredients in pharmaceutical formulations.T here are manys tudies reported in the literature using electrochemical techniques for simultaneous determinations by voltammetric detection on various types of workinge lectrodes [2][3][4][5][6][7][8].When electroanalytical methodsa re coupled to flow injection analysis (FIA), therea re even more advantages for the determination of electroactivec ompounds in comparison with voltammetric techniques using stationary detection mode.T he methods developed by FIA with electrochemical detection are faster and the passage of solution on the working electroder educes its surface fouling (or contamination) and increases the reproducibility of analyses.H owever, there are few studies in the literature using FIA systems with electrochemical detectionf or simultaneous determinations of drugs because the conventional amperometric detection mode (application of aconstant potential) is not selective.I nr ecenty ears,t he multiAbstract:T his work presents as imple,f ast and low-cost methodf or the simultaneous determination of three drugs by flow-injection analysis with multiple-pulse amperometric (MPA) detectionu sing aw all-jet flow cell with ab oron-doped diamond electrode.T he amperometric determination of caffeine (CF), ibuprofen (IB) and paracetamol (PC)w as performed by the application of af our-potential waveform using the MPAt echnique. PC is oxidized at E 1 (1.20 V/70 ms) and thus selectively detected;P Ca nd CF are oxidizeda tE 2 (1.49 V/40 ms);P C, CF and IB are oxidized at E 3 (1.70 V/70 ms);a nd E 4 (1.80 V/100 ms) is appliedf or electrode cleaning. The subtraction of currents obtaineda tt he differentp otentials did not provide accurated eterminations of CF and IB,t hus it was required to investigate correction factors to determine CF and IB without the interference from PC and CF usingt he respectivea mperometric signals obtained at E 2 and E 3 .T he proposed method was successfully appliedf or the determinatio...

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