Imidazolium-based ionic liquids as modifiers of carbon paste electrodes for trace-level voltammetric determination of dopamine in pharmaceutical preparations

Abstract

Abstract A simple approach for preparing sensitive and reliable working electrodes for the trace-level determination of dopamine (DA) is described. Carbon paste electrodes (CPEs) were bulk modified with two types of imidazolium based ionic liquids, namely 1-ethyl-3-methylimidazolium 1,1,2,2-tetrafluoroethanesulfonate ([emim][CHF2CF2SO3]) and 1-ethyl-3-methylimidazolium thiocyanate ([emim][SCN]), and the analytical performance of the resulting electrodes (CPE, [emim][CHF2CF2SO3]-CPE, [emim][SCN]-CPE) for the determination of DA was compared. Based on cyclic voltammetry (CV) for characterization and direct anodic square wave voltammetry (SWV) for quantifications, the most pronounced DA signal was obtained with [emim][CHF2CF2SO3]-CPE. Various experimental parameters were optimized including the pH of the supporting electrolyte and the amount of modifier incorporated into the carbon paste. For an analytical purposes 0.1 mol dm−3 phosphate buffer solution pH 5.8 was selected, because the DA peak was well-shaped and the most intensive. Under optimized conditions and using [emim][CHF2CF2SO3]-CPE as a working electrode, a linear relation between the oxidation current and the concentration of DA was obtained for the range of 0.020 to 0.28 μg cm−3; the relative standard deviation (RSD) did not exceed 1.5%, and evaluated detection (LOD) and quantitation (LOQ) limits in model solutions were 0.006 μg cm−3 and 0.020 μg cm−3, respectively. Interferences from ascorbic (AA) and uric (UA) acid did not affect the DA signal intensity to a great extent. The developed SWV method was successfully applied for the determination of DA in infusion solutions. The results for the samples were in good agreement with the values declared by the producer in all cases with RSDs below 1.3%.