Quantification of ultra-trace molybdenum using 4-amino-5-hydroxynaphthalene-2,7-disulfonic acid monosodium salt as a chromogenic probe.

A simple, ultrasensitive, nonextractive spectrophotometric method has been developed for the assay of Mo(VI), which involves Mo-catalyzed oxidation of 4-amino-5-hydroxynaphthalene-2,7-disulfonic acid monosodium salt (AHNDSA) by H(2)O(2) in acetic acid/sodium acetate buffer yielding an intense pink colored product with λ(max) of 540 nm. Beer's law is obeyed in the range of 10-240 ng/ml with molar absorptivity of 3.0137×10(5)L mol(-1)cm(-1).