Catalytic spectrophotometric determination of Mo(VI) in water samples using 4-amino-3-hydroxy-naphthalene sulfonic acid

In the present work, a sensitive, and simple kinetic method was developed for the determination of trace amounts of Mo(VI) based on its catalytic effect on the oxidation of 4-Amino-3-hydroxy-naphthalenesulfonic acid (AHNA) with H2O2. To optimize the parameters affecting the aforementioned system, the reaction was followed spectrophotometrically by tracing the oxidized product at 475 nm. The absorption of the solution in the presence and absence of the molybdenum ion in different conditions was compared. The optimum reaction conditions were: 9 mmol L−1 AHNA, 35 mmol L−1 H2O2, 27 mmol L−1 acetate buffer with pH = 5.3 at temperature 40 °C for 30 min. A 0.02% (w/v) di-ethylene tri-amine penta acetic acid (DTPA) was used as a masking reagent for confirming selectivity. The calibration curve was linear in the range 0.1-4.0 ng mL−1 with a correlation coefficient of 0.999 and the detection limit was 0.04 ng mL−1 (n = 15) based on the 3σbl/m. The proposed method was used for the determination of molybdenum in the different water and waste water samples.