Asymmetric logistic peak as a suitable function for the resolution of highly asymmetric voltammograms in non-bilinear systems.

The asymmetric logistic peak is tested as a new function for the parametric signal fitting (PSF) of highly asymmetric electrochemical signals in non-bilinear datasets, such as those obtained in linear sweep voltammetry (LSV) or in the presence of irreversible electrochemical processes. This new multivariate curve resolution strategy (PSF-ALPA) is successfully applied to LS voltammograms measured for the Cd(II)-glutathione system with a hanging mercury drop electrode, where Cd(II) is reversibly reduced, and to differential pulse voltammograms (DPV) measured at a glassy carbon electrode, where Cd(II) reduction becomes irreversible. Matrix augmentation by using LS voltammograms measured at different scan rates provides good results and encourages the development of ALPA methodology for third order data.

Voltammetric determination of dopamine at a zirconium phosphated silica gel modified carbon paste electrode.

Zirconium phosphated amorphous silica gel (devoted briefly as Si-ZrPH) modified carbon paste electrode (CPE) was used for detection of dopamine (DA) in the presence of ascorbic acid (AA) and uric acid (UA). Cyclic voltammetry demonstrated improved reversibility of the DA on the modified electrode. Cyclic voltammetry of Fe(CN)(6)(3-/4-) as a negatively charged probe revealed that the surface of the Si-ZrPH modified CPE surface had a high density of negative charge. As a result, the modified carbon paste electrode could inhibit the voltammetric response of AA and UA while the redox reaction of dopamine was promoted. Based on this, a selective method has been developed to detect DA in the presence of 2500 and 1000 time higher concentration of AA and UA, respectively. The effect of various experimental parameters on the voltammetric response of dopamine was investigated. Under the chosen conditions, the differential pulse voltammetry peak current was found to be linear with DA concentration in the ranges of 0.04 to 50 microM and 50 to 400 microM. The detection limit of the proposed method in the presence of 100 microM of AA and 40 microM of UA was found to be 0.02 microM for DA determination. Satisfying results are achieved when detecting the DA in injection and human serum samples.

Selective response of dopamine in the presence of ascorbic acid on carbon paste electrode modified with titanium phosphated silica gel.

Titanium phosphate grafted on the surface of silica gel (devoted briefly as Si-TiPH) was synthesized and used as bulk modifier to fabricate a renewable three-dimensional chemically modified electrode. The Si-TiPH bulk modified carbon paste electrode was used for the selective determination of dopamine (DA) in the presence of ascorbic acid (AA). The modified electrode offers an excellent and stable response for the determination of DA in the presence of AA. The differential pulse voltammetry peak current was found to be linear with the DA concentration in the range 2 x 10(-7) to 1 x 10(-6) and 2 x 10(-6) to 6 x 10(-5) mol L(-1). The detection limit of the proposed method in the presence of 2.0 x 10(-5) M of AA was found to be 4.3 x 10(-8) mol L(-1) for DA determination. The proposed method was successfully applied for the determination of DA in injections.