as described above was carried out according to theprocedure described in
5 mL of the sample was pippeted into the electrochemical cell thermostated to 40 ◦C and the following reagents were added: 1.5 mL3 mol L−1 KNO3 + 0.5 mL 0.2 mol L−1 DTPA + 2 mL 0.5 mol L−1 MES buffer (pH 6.1)