Spectroelectrochemistry at screen-printed electrodes: determination of dopamine

A new device to perform spectroelectrochemical measurements in the UV/visible spectral region using screen-printed electrodes has been developed. Neurotransmitter dopamine has been selected as a proof of concept of the capabilities of the new device. The results obtained have allowed us both to study the oxidation mechanism of dopamine and to carry out the spectroelectrochemical detection of this neurotransmitter. Differences in dopamine oxidation mechanism have been observed depending on the initial concentration. Thus, dopamine concentrations lower than 10(-3) M led to a higher generation of dopaminochrome and its derivatives with a band centered at 305 nm, which was the best wavelength to determine dopamine spectrophotometrically at these concentrations. However, if dopamine concentration is higher than 10(-3) M, dopaminoquinone is stable enough to use its maximum of absorbance, 395 nm, to detect this neurotransmitter. Dopamine concentration can also be calculated from the electrochemical data in spectroelectrochemistry, the results being comparable to that obtained from spectroscopic data. Comparison between spectrophotometric and electrochemical determinations demonstrates that the two methods measure this analyte indistinctively, proving that spectroelectrochemistry represents an autovalidated technique. Partial least-squares regression has also been used, obtaining good results in the full dopamine concentration range. Finally, as spectroelectrochemistry is an intrinsically trilinear technique, PARAFAC has been used to study the effect of probable interfering species.