THE EFFECT OF ADDITION OF FLY ASH AND LASER RADIATION ON CARBON BASED ELECTRODE FOR ANALYSIS OF DOPAMINE IN THE MIXTURE WITH ASCORBIC ACID USING VOLTAMMETRY

• Main Author: Sri Rahayu, Ria
• Format: Dissertations
• Language: Indonesia
• Subjects: Kimia
• Online Access: https://digilib.itb.ac.id/gdl/view/34227
• Institution: Institut Teknologi Bandung

Dopamine (DA) is a catecholamine compound which plays an important role as a neurotransmitter in the central nervous system. DA levels are related to several diseases such as Schizophrenia and Parkinson. Consequently, the determination of DA and related cathecolamines is necessary in neurochemistry and brain science studies. Therefore, the development of an accurate, fast, and simple method for the determination of DA becomes very important. Electrochemical methods such as voltammetry can be used for the determination of DA because DA is an electroactive compound. However, the voltammetric determination of DA is complicated by the presence of relatively high concentration of ascorbic acid (AA) in body fluids. AA is oxidized at a potential close to the potential oxidation of DA at most solid electrodes. As a result, the overlapping voltammetric response between DA and AA severely hinders the accurate determination of DA. Development of electrodes for the determination of DA in samples containing AA remains one of interesting topic to be developed in the field of electroanalytical chemistry. Various electrode modification methods such as coating electrode surface with polymer, adding electrocatalyst onto electrode surface, and using enzymes as biocatalyst have been studied to separate DA and AA peaks. However, some of these electrodes have drawback such as the use of expensive modifier, complicated modification process and difficult renewal process of electrodes. Therefore, development of modified electrode that can be used to selectively analyze DA in the present of AA is still necessary. Based on previous studies on the use of zeolite and silica gel for the modification of carbon paste electrode (CPE), in this study fly ash (FA) was used as modifying agent for CPE for voltammetric determination of DA. FA is an interesting material composed mainly of aluminosilicate as its main components and is expected to behave similar to zeolite and silica gel as CPE modifier. In this research, we studied the effect of the addition of FA on CPE for voltammetric determination of DA in the presence of AA. The addition of FA on CPE could increase the selectivity of DA determination in its mixture with AA. The oxidation peak of AA on CPE was very close to the oxidation peak of DA and the peaks could not be separated. On CPE-FA the oxidation peak of AA decreased significantly while the oxidation peak of DA still had similar height to that on CPE. In phosphate buffer solution (PBS) of pH 7 some of silanol functional group in FA have been deprotonated that produce negatively charged electrode surface. At this pH, DA having pKa1 of 8.9 is positively charge and will be attracted to the surface of the electrode, while AA is negatively charged (pKa1 = 4.02) and will be rejected by the electrode. The optimum conditions for determination of DA using CPE-FA have been investigated. The optimum pH for DA determination was 7.0. Linear calibration curves for DA are obtained over the concentration range of 1 µM - 1 mM with a detection limit (3?) of 0.22 µM. This electrode has been applied to determine DA levels in blood plasma samples. The accuracy of DA measurement in blood plasma samples was very good with percent recoveries between 99.93 to 100.06%. This electrode cannot be used for in vivo determination of DA. However, an understanding of the performance of this electrode is expected to be the basis for miniaturization of the electrode as a sensor for in vivo determination of DA in body fluids. We also study the effects of laser irradiation on the performance of CPE-FA and Glassy Carbon (GC) electrode for DA and AA determination. Laser irradiation on CPE-FA increased heterogeneous electron transfer rate of both DA and AA oxidation at the electrode surface, which increase the sensitivity of DA determination. However, the selectivity of DA determination in the presence of AA was poor because oxidation peak of AA shifted to a more negative potential so that the oxidation peak of both DA and AA cannot be separated. The increase in the rate of electron transfer of DA an AA was due to elimination of impurities and formation of active site on the electrode surface. Irradiation intensity affects the performance of CPE-FA electrode. As the intensity of laser irradiation increased, the oxidation peak current was also increase but high intensity laser irradiation damage the surface of CPE-FA electrode. In this study laser intensity of 40 mJ/pulse was used for CPE-FA electrode. DA and AA oxidation at CPE-FA electrode was found to be controlled by diffusion Similar results were found on GC electrode. Laser irradiation on GC electrode also increased the rate of electron transfer of DA and AA oxidation. Since GC was mechanically stronger than CPE-FA, irradiation intensity of 100 mJ/pulse was used. DA oxidation at unirradiated GC electrode is controlled by both adsorption and diffusion process. At irradiated GC electrode, the diffusion process becomes more dominant. Oxidation of AA is controlled by a diffusion process at both irradiated and unirradiated GC electrode. Oxidation peaks of both compounds occured at a more negative potential. The peaks were well separated and could be used to determine DA in the presence of AA.