Electrode preconditioning

A device comprising

• an electrochemical cell having a working electrode and a pseudo reference electrode;
• an electroactive substance capable of undergoing an electrochemical reaction when in contact with a sample of bodily fluid, the electroactive substance comprising an electrocatalyst and a mediator;
• a potentiostat for applying a potential between the working and pseudo reference electrodes;
• a controller programmed to operate the potentiostat to apply firstly a time varying preconditioning potential between the working and pseudo reference electrodes consisting of carrying out at least one but no more than two preconditioning scans, and subsequently to apply a measuring potential between the working and pseudo reference electrodes, wherein in the or each preconditioning scan the applied potential is decreased from substantially 0 to a first applied potential of no more than −0.5V and then increased to a second applied potential of at least 1.1V;
• and
• means for measuring the current across the cell, wherein said means is configured to measure the current during application of the measuring potential.