The article deals with the design of handheld potentiostat instrument utilizing an ASIC. It briefly shows complete system and control software as well. The FPGA is used to generation of the measuring potential waveform and for communication with AD and DA converters and with PC. The designed ASIC that forms the core of the instrument consists of an output buffer and a current to voltage converter with selectable measurement range. The reached parameters of the ASIC are presented as well.