Determination of Mn(II) in tap water with 2-hydroxy-1-(2-hydroxy-4-sulfo-1-naphthylazo)-3-naphthoic acid by catalytic analysis

Catalytic analysis of Mn(II) in tap water using 2-hydroxy-1-(2-hydroxy-4-sulfo-1-naphthylazo)-3-naphthoic acid (NANA) has been described. The decomposition reaction of NANA with hydrogen peroxide was catalyzed by Mn(II) in alkaline medium. The sensitivity of the method was very high; however, the selectivity was not sufficiently high for the determination of Mn(II) in tap water. Therefore, the effect of some masking agents was examined. Triethanolamine was selected in spite of decreasing the sensitivity for Mn(II). The optimum conditions for Mn(II) determination in the presence of triethanolamine were as follows: pH 10.4, CAPS (0.02 M) as buffer reagent, NANA (6.85x10(-5) M), triethanolamine (0.27 M), hydrogen peroxide (0.5%), and temperature 30 degrees C. As the result, the RSD was 5.4% (n=6) at 0 ppb of Mn(II). The detection limit was 0.06 ppb (S/N=3). A calibration curve was made between In(A(1)/A(6)) and Mn(II) concentration, where A(1) and A(6) were the absorbances of NANA at 1 min and 6 min after the start of the decomposition reaction, respectively. The determination range was 0.2 ppb to 1.0 ppb. Diversions, e.g., Fe(III) up to 100-fold, and Cu(II) and Zn(II) up to 125-fold the Mn(II) concentration (0.8 ppb), were tolerated fbr the determination of Mn(II) by using triethanolamine as the masking agent. The results of trace Mn(II) determination in tap water showed good agreement with the values obtained by graphite furnace AAS.