The present invention relates to an electroanalytical instrument for determining by amperometry (eg chronoamperometry) the presence or quantity (eg concentration) of an analyte in an aqueous sample, comprising a sealed housing, an elongate pivotal arm mounted on the sealed housing, wherein the elongate pivotal arm houses a potentiostat, and a pivotal forearm joined pivotally to the elongate pivotal arm, which is connectable to an electrochemical sensor. By flexing the pivotal forearm, the electrochemical sensor may be electrically connected to the potentiostat. By flexing the elongate pivotal arm, the electrochemical sensor is immersed in the aqueous sample in the sealed housing.