Rapid spectrophotometric determination of water-soluble manganese in soils using 2-(5-bromo-2-puridylazo)-5-diethylaminophenol

ABSTRACT This paper reports a spectrophotometric method for determining water-soluble manganese in soils. 2-(5-Bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) is used as a chromophoric reagent. It reacts with manganese in H2O – EtOH medium of PH 8.5 to form a purple complex having an absorption maximum at 558 nm and molar absorptivity of 1.06 × 105 L-mol-1.cm-1. Beer's law is obeyed in the concentration range of 0 to 10 ±g of manganese per 25 ml of solution. The interference in the determination of manganese and the method of elimination have also been investigated in detail. The mole ratio of manganese and 5-Br-PADAP in the complex was estimated to be 1:2 by the continuous variation and the mole ratio methods. The proposed method is simple and rapid, and the results of the determination were reasonably accurate. The well-known and often-used spectrophotometric method for determining manganese, which is based on the colored permanganate ion, is highly selective but rather insensitive (Gottschalk 1965; Gaunt and Diehl 1972). The use of 5-Br-PADAP has also been recommended (Wei et al. 1981). A brief review of analytical applications of this reagent has been given by Wei et al. (1980). This communication describes optimum experimental conditions for formation of the complex and its application to determination of water-soluble managanese in various soils.