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
K. Watanabe et al., 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, BUNSEKI KAG, 49(8), 2000, pp. 599-604
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.