A composition suitable for use in an electrochemical sensing method, said composition comprising (i) a transition metal salt; (ii) an electrode area normalising agent having a current which is dependent on electrode area; and (iii) a wetting agent. Also provided is a device comprising - an electrochemical cell having a working electrode and a pseudo reference electrode; a composition according to the invention; means for applying a voltage across the cell; and means for measuring the resulting current across the cell. The device can be used in the electrochemical diagnosis of ischemia.
