A simple spectrophotometric method for the determination of trace levels of molybdenum in industrial, environmental, biological and soil samples using benzoylacetone-benzoylhydrazone

Abstract

A very simple, ultra-sensitive and highly selective non-extractive spectrophotometric method for the determination of trace amounts of molybdenum(VI) in solution using benzoylacetone-benzoylhydrazone (Bzac-BH) has been developed. Bzac-BH reacts in a slightly acidic solution (0.0003–0.002 M H₂SO₄) with molybdenum(VI) to give an orange chelate which has an absorption maximum at 447 nm. The reaction is instantaneous and the absorbance remains stable for over 12 h. The average molar absorption co-efficient and Sandell's sensitivity were found to be 6.3 × 10⁵ L mol⁻¹ cm⁻¹ and 15 ng cm⁻² of molybdenum(VI), respectively. Linear calibration graphs were obtained for 0.05–2 mg L⁻¹ of molybdenum(VI). The stoichiometric composition of the chelate is 1 : 1 (Mo : Bzac-BH). A large excess of over 50 cations, anions and complexing agents (such as chloride, phosphate, azide, thiosulfate, thiourea, SCN⁻, etc.) do not interfere with the determination. The developed method was successfully used in the determination of molybdenum levels in several Standard Reference Materials (alloys and steels) as well as in some environmental waters (inland and surface), biological samples (human blood and urine), soil samples, solutions containing both molybdenum(V) and molybdenum(VI) and complex synthetic mixtures. The method has high precision and accuracy (s = ±0.01 for 0.5 mg L⁻¹).