Flow-injection spectrophotometric catalytic determination of manganese in plants exploiting the aerial oxidation of diphenyl carbazone

Abstract

The catalytic effect of Mn(II) on the aerial oxidation of diphenylcarbazone (DFC) becomes very pronounced in the presence of triethanolamine (TEA), whereas the influence of other potential interferants is strongly reduced. This feature was exploited to develop an improved flow-injection procedure for manganese determination in plant digests. In view of the high variability of manganese contents in the sample batches, an approach involving two sampling loops was implemented to widen the dynamic range. The proposed system handles about 70 samples per hour, requires only 0.13 mg DFC and 85.7 mg TEA per determination, and yields reproducible signals (r.s.d. of peak heights usually<2%) within two different concentration ranges (0.10–0.80 and 0.50–4.00 mg l −1 Mn). Detection limit is 0.03 mg l −1 Mn in the digest (3 μg g −1-dry basis). Results are in agreement with flame atomic absorption spectrometry. A noteworthy feature of this procedure is the negligible progress of the uncatalyzed reaction.