The enzymatic reactor was a 4 X 40 mm steel column filled with immobilised oxalate oxidase (purified from barley seeds, SIGMA, Germany). The oxidase was immobilised by shaking
5 U oxidase with 150 mg VA Epoxy (Riedel-de-Haen, Germany) in 5 ml phosphate buffer (pH 5.0) for 24 h. HZ02 was detected with an amperometric detector PED 300 (Gynkotek)