Fig. 4
Effect of mobile phase composition on PCNB (a) and superoxide ion response (b). Both superoxide ion (O2−) and PCNB signal increased roughly by a factor of 300 and 30, respectively, when we changed the mobile phase from a mixture of methanol and water with 0.1% formic acid and 2 mM ammonium formate to a mixture of methanol and water. Mobile phase 1: methanol and water with 0.1% formic acid and 2 mM ammonium formate. Mobile phase 2: methanol and water