An electrochemical analyzer based on a potentiostat/galvanostat (PG004) was developed and applied to perform in situ Pb²⁺ and Cd²⁺ determination in water samples with on-line data transmission, and a global positioning system (GPS), to acquire the geographical coordinate of the place being monitored. For this, a flow-batch analysis (FBA) and a thermostated electrochemical flow cell (EFC) coupled with a boron-doped diamond electrode (BDD) were developed to measure these ions by employing square-wave anodic stripping voltammetry (SWASV). To study the Pb²⁺ and Cd²⁺ ions by in situ analysis, mainly for temperature variation, the PG004 was evaluated and the limits of detection were 0.08 μg L⁻¹ and 0.18 μg L⁻¹, respectively, for simultaneous analysis. Then, the PG004 was used for in situ determination of analytes in lake water samples, and voltammograms with good resolution and low noise were obtained. Recoveries ranged from 93.3% to 109%, and the waste generated was as low as 700 μL per determination. The accuracy of the method was checked by determination of Cd²⁺ and Pb²⁺ in certified water (NIST), t-unpaired test was applied for n = 3, and the values found were in close agreement at a confidence level of 95%. Besides the geographical coordinates obtained by using a GPS receiver, and experimental data sent via wireless, the device used a solar board as renewable energy. The developed system proved to be a useful tool to measure Pb²⁺ and Cd²⁺ in lake samples with a fast, on-line, and environmentally friendly analytical method.