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 microanalyses. 2-Hydroxy-1-(2-hydroxy-4-sulfo-1-naphthylazo) -3-naphthoic acid (NANA) is an excelent reagent used for the catalytic analysis of manganese(II). The detection limit for the determination of manganese(II) with NANA was 0.15 ppt. However, an improvement in the sensitivity for the determination of manganese(II) was expected by purifying of NANA as an indicater reagent. A wide variety of methods have been proposed and used for die purification of reagents; liquid-liquid extraction is the most extensively used method. 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 has a large distribution ratio. Five micrograms of manganese(II) were recovered 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. Furthermore, purified NANA was applied to a catalytic analysis. The color-fading rate [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 10 min after starting the reaction, respectively. Since In(A(1)/A(10)) is proportional to the manganese(II) concentration; it was been confirmed that manganese(II) in NANA was removed. When purified NANA was used, die calibration 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 conventional procedure.