Removal of a manganese(II) impurity in 2-hydroxy-1-(2-hydroxy-4-sulfo-1-naphthylazo)-3-naphthoic acid by a simultaneous forward and back-extraction method

To remove impurities from a reagent is very important in the field of micro analyses. 2-Hydroxy-1-(2-hydroxy-4-sulfo-1-naphthylazo) -3-naphthoic acid ( NANA) is an excelent reagent used for the catalytic analysis of manganese(I I). The detection limit for the determination of manganese(II) with NANA wa s 0.15 ppt. However, an improvement in the sensitivity for the determinatio n of manganese(II) was expected by purifying of NANA as an indicater reagen t. A wide variety of methods have been proposed and used for die purificati on of reagents; liquid-liquid extraction is the most extensively used metho d. In this paper, the condition for removing manganese(II) from NANA by the simultaneous forward and back-extraction method is examined for purpose of purifying NANA. This method is similar to a liquid-membrane method (uphill transport). 5,7-Diiodooxine was used as an extraction reagent because it h as a large distribution ratio. Five micrograms of manganese(II) were recove red perfectly from 100 ml of a 1.2 x 10(-3) M-NANA solution with 1.5 M-HNO3 solvent at a stirring time of 40 min under the optimum conditions. Further more, purified NANA was applied to a catalytic analysis. The color-fading r ate [In(A(1)/A(10))] of unpurified NANA was 0.061 and that of purified NANA was 0.038, where A(1) and A(10) are the absorbances of NANA at 1 min and 1 0 min after starting the reaction, respectively. Since In(A(1)/A(10)) is pr oportional to the manganese(II) concentration; it was been confirmed that m anganese(II) in NANA was removed. When purified NANA was used, die calibrat ion curve of manganese(II) was liner over the range 0 similar to 2 ppt, and its detection limit was 0.10 ppt It was greatly improved compared to the c onventional procedure.