A highly selective and sensitive spectrophotometric method for the determination of selenium using 2-hydroxy-1-napthaldehyde-orthoaminophenol

Abstract

A very simple, ultra-sensitive and highly selective non-extractive spectrophotometric method for the determination of trace amounts of selenium using 2-hydroxy-1-napthaldehyde-orthoaminophenol (HNA-OAP) has been developed. HNA-OAP reacts in slightly acidic (7 × 10⁻⁶ to 3.5 × 10⁻⁵ M H₂SO₄) aquatic media with selenium(IV) in 40% N,N-dimethylformamide (DMF) to produce a highly absorbent orange red chelate, which has an absorption maximum at 509 nm. The absorbance intensity of the metal–chelate reaches a constant value (after heating for 5 min at 45 ± 5 °C) within 15 min and remains stable for over 24 h. The average molar absorption coefficient and Sandell's sensitivity were found to be 6.30 × 10⁵ L mol⁻¹ cm⁻¹ and 10 ng cm⁻² of Se, respectively. Linear calibration graphs were obtained for 0.02–7.0 mg L⁻¹ of Se, having a detection limit of 1.0 μg L⁻¹, the quantification limit of the reaction system was found to be 10 μg L⁻¹, and the RSD was 0–2%. The stoichiometric composition of the chelate is 2 : 3 (Se : HNA-OAP). A large excess of over 60 cations, anions and complexing agents does not interfere in the determination. The method was applied successfully in the determination of selenium in several standard reference materials (alloys, steels, sediments, tea and bovine liver) as well as in some environmental waters (portable and polluted), biological samples (human blood, urine and hair), soil samples, food samples, pharmaceutical samples, solutions containing both selenium(IV) and selenium(VI) and complex synthetic mixtures. The method has high precision and accuracy (s = ±0.01 for 0.5 mg L⁻¹).