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The voltammetry method is a field of electrochemistry that measures electric current at a certain potential, which can be used to determine the concentration of inorganic and organic compounds that can be oxidized or reduced. In this research, the differential pulse voltammetry (DPV) technique has been used to determine the content of Pb(II). The carbon paste electrode (CPE) and ferrocene-modified carbon paste electrode (CPE-Fc) were used as working electrodes. This study aims to improve the sensitivity of Pb(II) measurement. Two parameters were optimized were ferrocene composition and scan rate. The validation parameters involved the linear concentration range, detection limit, quantization limit, precision and accuracy. The optimum ferrocene composition was found at 6%, and scan rate was 15 mV/s using CPE, increase to 20 mV/s using CPE-Fc. The validation results showed the linearity using CPE-Fc wider than CPE at the peak potential of 0.515 V. The detection and quantization limit values using CPE were 0.1551 µg/L and 0.1556 µg/L, and down to 0.1089 µg/L and 0.1090 µg/L using CPE-Fc. The precision determination for both of CPE and CPE-Fc had good results, indicated by the Horwitz ratio less than two. Percentage of recovery using CPE-Fc of 85.59 8.18%. CPE-Fc at the optimum measurement conditions was used to determine the levels of Pb(II) in kepok banana, and the result was obtained 4.4306 0.0009 mg/kg. The level of Pb content was found to exceed the established threshold based on Standard National Indonesia (ISN) No. 7387:2009 which is 0.5 mg/kg.

Voltammetry is an electroanalytical method measure current as a function of applied potential. The working electrode in the voltammetry method dramatically affects the result of the electrochemical analysis. Modification of the working electrode can improve measurement performance. In this research, the carbon paste electrode (CPE) was modified with Bentonite (CPEB) to determine copper's level using differential pulse voltammetry technique. CPE and CPEB were used as working electrodes, handmade Ag/AgCl as a reference electrode, and Pt wire as the counter electrode. The measurement parameters were optimized, including the composition of bentonite in carbon paste and scan rates. Furthermore, the measurement conditions were validated, involved linear concentration range, detection limit (LoD), the limit of quantization (LoQ), repeatability, and recovery. The results showed that bentonite's optimum composition was 40% of the total weight of graphite and activated bentonite. The scan rate optimum for Cu2+ measurement was obtained at 20 mV/s with CPE and became faster to be 25 mV/s with CPEB. The linearity of the standard solution measurement of Cu2+ using CPE was in the range of 5 to 100 μg/L and changed to 5 to 500 μg/L using CPEB. LoD and LoQ values of standard solution Cu2+ measurement with CPEB were slower than CPE. The Horwitz ratio calculation was smaller than two for both CPE and CPEB. The recovery of Cu2+ standard measure in sample solution as the matrix was obtained 93,49 ± 6,39%. According to the Decree of the Ministry of Health Number, the level of Cu2+ in the tomato sample was found 6.019 ± 0.69 mg/kg, which is over than threshold value of Cu2+ (5 mg/kg) 03725/B/SK/VII/89.