Flow injection determination of trace amounts of manganese by catalytic oxidation of N-phenyl-p-phenylenediamine with cumenehydroperoxide

A sensitive catalytic method is proposed for the determination of manganese using a FIA system. The method is based on the catalytic effect of manganese(II) on the oxidation of N-phenyl-p-phenylenediamine (PPDA) in the presence of cumenehydroperoxide as an oxidant; PPDA is oxidized to a yellow compound at pH 10.5 by the oxidant, and this compound is then converted to a blue-green compound (lambda(max)=775 nm) with a higher absorbance than the yellow compound in a strong acidic solution. Higher sensitivity could be attained by adding triethylenetetramine (trien) as an activator. A linear calibration graph for manganese(II) was obtained over the range of 2 similar to 50 ppt and the reproducibility was satisfactory with a relative standard deviation of 1.2% for 10 ppt manganese (n=10) at a sampling rate of 27 per hour. By using cumenehydroperoxide in place of hydrogen peroxide, which was frequently used in most indicator reactions for catalytic methods based on the redox reaction, the blank values could be kept low. The proposed method was successfully applied to the determination of manganese in tap water, river water and standard river water samples.