The organometal solution to produce TiO₂ is titanium tetra-isopropoxide (TTIP) which is mixed by ethanol 99%, acetylacetonate, and acetate acid. These material refluxed at a temperature of 80°C for 3 hours. Subsequently, sol TiO₂ was calcined at 500°C for 3 hours to form TiO₂ anatase crystal. This crystal is crushed by agate mortal and sieved to obtain smooth the TiO₂ nanoparticles [37]. Then, TiO₂ was variated to obtain the mass optimation i.e. 0.01 g, 0.05 g, and 0.1 g. Then, it was mixed by 0.7 g carbon and 0.3 mL paraffin oil (d = 0.88 g.cm⁻³) followed heating at the temperature of 80°C to sticky between particles. Mobilization in wall glass, we rinse the probe glass by distilled water and acetone followed sonification for 15 minutes. Finally, the material was entered in probe glass with diameter 3 mm, connected by Cu wire as a conductor and also tip electrode was polished [2].

Voltammetric detection of fipronil was conducted using a potentiostat (DY2100B-Digi.Ivy) with three electrodes system where the TiO₂-CPE nanocomposites as the working electrode. Meanwhile, a platinum (Pt) and Ag/AgCl wires were used as the counter and reference electrodes, respectively. The optimation response electrode determined by using K₃[Fe(CN)₆] that role for increasing a solution's redox potential (E°' ~ 436 mV at pH 7). In addition, the sample tests under 1.0 M (NH₄)₂SO₄ electrolyte due to is a strong electrolyte, stability in osmotic effect, and dissolves 100% in aqueous solution. The fipronil concentration was applied in 10⁻⁶, 10⁻⁵,10⁻⁴,10⁻³,10⁻², and 10⁻¹ μM to determine the linearity areas and LOD. The real sample was tested by mixing electrolyte solution for identifing peak current characteristic fipronil in the real sample. We also determination of repeatibility for 30 times and tested lifetime electrode for 23 days.

The morphology of the nanocomposites was examined using a Scanning Electron Microscopy JEOLJSM-6510LV. Meanwhile, the phase and crystallinity properties were characterized via X-ray diffraction spectroscopy (XRD) using Philips X-ray diffraction spectrometer with a CuKα irradiation (λ=0.154 nm) and scan rate as low as 2° min⁻¹.

The anatase TiO₂-CPE nanocomposites has been successfully prepared via sol-gel method. Due to phase purity of anatase TiO₂ has a high-stability and electron transfer in the electrochemical system. Fig. 1 exhibits the XRD pattern anatase TiO₂, there are at least 9 peaks spectrum characteristics based on JCPDS file no. 21-1272, namely 25°, 38°, 48°, 52°, 54°, 64°, 69°, 70°, and 76° with Bragg diffraction at the crystal field of (101), (004), (200), (105) (211), (204), and (215), respectively. These data have been compared with TiO₂ P25 standard [2].

We then observed the anatase TiO₂-CPE nanocomposites using SEM instrument. The unique microstructures were displayed that the anatase TiO₂ successfully incorporated in carbon matrix (Fig. 2). In same times, high-contacted a solid-state reaction by adding paraffin as attach agent. We can conclude the anatase TiO₂ nanocomposites were homogeneously distributed in the carbon paste matrix. The TiO₂ given shine characteristics caused the inducing of electron to make a high-atom number easy for emitting energy. We discover the approximate size of TiO₂ nanoparticles in this study is 2 μm (Fig. 2).

The mass optimation aims to synergistic the anatase TiO₂ combined with carbon paste which applied electrochemical system. The high current response observed based on CV by variating mass of 0.01 g, 0.05 g, and 0.1 g TiO₂ sol-gel mixed pristine carbon in 0.1M K₃[Fe(CN)₆] as an electrolyte solution under scan rate of 0.1 V/s. The K₃[Fe(CN)₆] as naturally for increased separation of cathodic and anodic peaks and reversible characteristic for redox reaction. As Fig. 3, we discover the mass optimum TiO₂ anatase of 0.1 g with oxidation peak the Ip_a value of 1.13×10³ μA, Ep_a value of 0.1 V with reduction peak of Ip_c value of −0.96×10³ μA and Ep_c value of 0.34 V.

The high composition of anatase TiO₂ into the CPE matrix to increase performance the high TiO₂ concentration estabilized the optimum condition. Based on Fig. 3, the sample demonstrates an excellent electrochemical response with a high current peak. In addition, it can be remarked that the electron transfer process is extremely fast as indicated by a remarkably small difference in the redox potential. The electrode with a composition of 0.1 gram TiO₂ was the best electrode performance in electrochemical system causes the produce a maximum peak flow response when compared to other compositions. Finally, it is suitable to be used for measuring fipronil pesticide.

This parameter was conducted to compare electrochemical response of fipronil which is containing electrolyte and without the fipronil solution. The electrochemical profile can be seen in Fig. 4. Based on the measurement (see Fig. 4) exhibit that the determination of the electrochemical response without the fipronil did not reveal peak response if it compared with adding fipronil causes the (NH₄)₂SO₄ electrolyte solution did not react with analytes, stable, and high-electron transfer [38]. We discover the high-current response for 0.1 μM fipronil containing electrolyte has a good oxidation response with Ip_a value of 31.4 μA and Ep_a value of −0.15 V. The Ip_a value was produced based on electrode measurement responded fipronil pesticide which is an oxidation reaction.

The optimation the scan rate has been conducted by variating the of 0.05; 0.1; 0.2; and 0.5 V/s due to the faster scan rate in analyte measurements will be produced the high-current peak. The 1.0 μM fipronil shows the measurement rate has been increased when the high variation scan rate. This is due to the scan rate effect was reversibility concentration indirectly by measuring the apparent a standard rate constant for electron transfer from only cathodic (or anodic) polarization. In a few cases both cathodic and anodic [39]. Based on analyzed (Fig. 5), we obtain the optimum scan rate on 0.5 V/s with the Ip_a value of 31.7 μA and the Ep_a value of −0.15 V. The high scan rate has been produced proportional with the high scan rate.

The linearity of fipronil has been determined by plotting the variation concentration (10⁻⁶, 10⁻⁵, 10⁻⁴, 10⁻³, 10⁻², and 10⁻¹ μM) which is containing 1.0 M (NH₄)₂SO₄ as electrolyte between Ip_a value which produced from CV profile. Fig. 6 exhibits that the high concentration causes a high CV response. This phenomenon because of increasing fipronil concentration makes the increase ions produced to interact on the electrode surface. Based on the curve, the cathodic (reduction) potential not significantly produced because the (NH₄)₂SO₄ electrolyte containing fipronil only giving the oxidation response onto the working electrode (see Fig. 4). The TiO₂-CPE nanocomposites play a role for oxidation process sensing and high transfer electron in the electrochemical system. We then plot the linear line equation between Ip_a value with concentration to obtain the linearity area from the working electrode by the range of electrode performance detecting fipronil compound in low concentrations from 10⁻⁶, 10⁻⁵, and 10⁻⁴ μM. The unique performance is identified as the LOD in low concentration which is cannot be analyzed by highinstrumentation. The higher concentration proportional with increase in anodic current [40,41]. High concentration causes more fipronil ions to accumulate on the electrode surface so that the current result is also higher. We discover the determination of LOD value was 34.0×10⁻⁵ μM by multiplying 3 with standard deviation divided by the value of the slope. This phenomenon to obtain the lowest quantity of fipronil concentration that can be identified from the working electrode.

The repeatability test was conducted to exhibit the working electrode performance against the consistency of measurement. This treatment the TiO₂-CPE nanocomposites has been tested by using 1.0 μM fipronil containing 1.0 M (NH₄)₂SO₄ as the electrolyte. Fig. 8 depicts the results of repeatability working electrode that the high-performance of TiO₂-CPE stability for 30 times tested. The rate electrons transfer were stabilized on the electrode surface and oxidizing the fipronil compound. Based on this study (Fig. 8), we obtain the Ip_a value of 27.4 μA and calculating the standard of deviation (SD) of 2.512 and Relative Standard Deviation (RSD) is 0.8%. We declare that the TiO₂-CPE nanocomposites has stabilized due to the Horwitz value is obtained less than 2%.

Especially, we explore a lifetime of TiO₂-CPE to obtain the high-performance electrode for 23 days. The lifetime test performance has been carried out by using the same solution on the repeatability test. Extension lifetime electrode enforced for clarifying TiO₂-CPE to sensitivity against fipronil. Fig. 9 exhibits that the optimum performance electrode from 1 until 13 days relatively stable, while the 14 until 23 days the low-performance electrode. This condition that the longer electrode used causes thickening diffusion on the electron transfer system and limiting peak current. In addition, it has saturated on electrode pores causes the current diffusion. Meanwhile, if it will be enhanced the TiO₂-CPE nanocomposites should be annealing to remove the organic compound on the electrode surface.