The determination of dopamine or uric acid with the presence of other using square wave voltammetry

The aim of this study is to develop a new method in the simultaneous determination of dopamine (DA) and uric acid (UA) cations together with using square wave voltammetry. The first step was the investigation of the reduction behavior of DA and UA in media containing different supporting electrolytes. It was found that the most suitable media for the analysis were H2SO4 and phosphate buffers. The highest peak current for the compounds was found at pH 2,5. The pH value for the basic medium was chosen as 7,2. The analysis of DA and UA in acidic medium was carried out by the use of their peaks observed at +0,480 V and +0,620 V. The analysis of DA in the presence of UA was carried by standard addition method while the analysis of UA in the presence of DA was done by the calibration method. The analyses of the alkaline phosphate buffer medium at ph 7,2 were carried out by the use of the reduction peaks of DA and UA appeared at +0,140 V and +0,270 V respectively. The determinations were performed by the standard addition method. The initial studies were realized where [DA] / [UA] ratio was equal to 1. This ratio was changed afterwards and the best results was obtained when [DA] / [UA] = 5 at pH 2,5. In phosphate buffer medium the most satisfying results were observed when [DA] / [UA] > 1. However the studies carried out with different [DA] / [UA] ratios gave acceptable result for both media. The second stage was the use of a synthetic sample containing 9,76 x 10-6 M DA and 14,63 x 10-6 M UA. The results obtained were (9,72 ± 0,10) × 10-6 M for DA and (14,67 ± 0,10) × 10-6 M for UA in acidic medium . The % error was -0,41 for DA and 0,27 for UA. The results obtained in basic media with pH 7,2 were (9,70 ± 0,04) × 10-6 M and (14,61 ± 0,18) × 10-6 M respectively. The % errors for DA and UA were -0,61 and -0,14. The limits of determination (LOD) were 2,16 × 10-8 M and 4,14 × 10-8 M and limits of quantification (LOQ) were 6,48 × 10-8 M and 1,24 × 10-7 M for DA and UA in acidic media. These values were found to be 2,28 × 10-8 M and 2,13 × 10-8 M for LOD and 6,84 × 10-8 M and 6,39 × 10-8 M for LOQ in alkaline media with pH 7,2. The interference of various anions and cations was also investigated.Key Words: Dopamine, uric acid, square wave voltammetry, determination