Judul: Electrochemical Sensor for Detection of Chlorotalonil Residue in Grapes
Abstrak: The use of chlorothalonil in grapes as a pest control agent, could bring potential harm for health and the environment. Therefore it is necessary to test the residue of chlorothalonil pesticides in grapes as part of food safety control. Pesticide residue testing generally uses HPLC, GC-MS/MS dan LC-MS/MS. Although have high sensitivity, these technique require very expensive equipment, long analysis times, high sample volumes of reagents and competent testing personnel. Meanwhile, pesticide residues testing in the field generally required fast procedure, portable, and easy to use. Therefore, this research aims to develope testing methods for chlorothalonil pesticide residues with electrochemical sensors which can be an alternative method for testing chlorothalonil pesticide residues in grapes. In this study, a differential pulse voltammetry (DPV) technique was chosen using a glassy carbon electrode (GCE) with graphene oxide (GO) and poly 3,4- ethylenedioxythiopene (PEDOT:PSS). In this study GO synthesis was carried out using the modified Hummers method. The characterization results using Raman and FTIR spectroscopy showed the successful synthesis of GO from graphite. The results showed that the modified GCE treatment GO/PEDOT:PSS was significantly different from the unmodified GCE (p<0,05). The addition of composites to the modified electrode improved the performance of the sensor in detecting chlorothalonil. Meanwhile, the peak current of chlorothalonil reduction in GCE modified with GO and PEDOT:PSS composites with various ratios gave results that were not significantly different (p>0,05). Furthermore, the GO/PEDOT:PSS composite ratio (1:1) was determined as the best composite composition in this study. Chlorothalonil is only slightly soluble in Britton Robinson Buffer (BRB), so it is necessary to explore the use of electrolyte combinations with organic solvents. In this experiment, the ratio of BRB:ACN (1:1) was the optimum electrolyte ratio and pH 9 as the optimum pH. Analytical performance parameters observed in this study were reproducibility and stability resulted in %RSD < 5% which shows acceptable results. Based on the result of selectivity test from GCE/GO/PEDOT:PSS was selective for chlorothalonil from interferences such as ascorbic acid, calcium, calium, magnesium, natrium, and sucrose with the effect result of interference to chlorothalonil has not significantly different (p>0,05). In addition, there was a linear relationship in the chlorothalonil concentration range of 10-200 µM with a correlation coefficient of 0,9966 and a detection limit was 3 µM and a quantitation limit was 8 µM. Good accuracy was also demonstrated by the %recovery obtained from 97.77 – 103,61% and successful detection of chlorothalonil in grapes by the standard multiple point addition method of 273 µM or equivalent to 29,03 mg/kg. As a result of the confirmation test using GC-MS/MS, the detection result of the residual concentration of chlorothalonil in the grapes was 0.03 mg/kg. The measurement result of the electrochemical method were higher and significantly different from those with GC-MS/MS. The concentration values detected in this experiment were quite high above the allowable MRL (Maximum Residu Limit) and still give the respon false positive result. This is possible due to the interference of the complex matrix effect in the grape samples. Optimizing this electrochemical test, require a more extensive matrix effect test. However, the electrochemical
Keyword: Chlorothalonil, electrochemical sensor, graphene oxide, pesticide