High Sensitive and Selective Spectrophotometric Method for the Determination of Trace Level of Manganese in Some Real, Environmental, Biological, Soil, Food, Fertilizer and Pharmaceutical Samples Using Bis(2-hydroxy-1-naphthaldehyde) Orthophenylenediamine

A very simple, ultra-sensitive and highly selective non-extractive spectrophotometric method is present for the determination of manganese at trace level using bis(2-hydroxy-1-napthaldehyde) orthophenylenediamine (HNA-OPD-HNA) has been proposed as new analytical reagent for the direct non-extractive spectrophotometric determination of manganese(II). HNA-OPD-HNA reacts in a slightly acidic (0.000002-0.00001M H2SO4) with manganese (II) in 50% N, N-dimethylformamide (DMF) to produce highly absorbent an orange chelate which has an absorption maximum at 508 nm. The reaction is instantaneous and the absorbance remains stable for over 24 h. The average molar absorption co-efficient and Sandell’s sensitivity were found to be 4.89×106 L mol-1cm-1 and 10 ng cm-2 of manganese (II), respectively. Linear calibration graphs were obtained for 0.02-25 mg L-1 of manganese(II) having detection limit of 1 μg L-1 and quantification limit of the reaction system were found to be 10 μg L-1 and RSD 0-2%. The stoichiometric composition of the chelate is 1:1 (Mn: HNA-OPD-HNA). A large excess of over 60 cations, anions and complexing agents (like, chloride, phosphate, azide, tartrate, oxalate, SCN- etc.) do not interfere in the determination. The developed method was successfully used in the determination of manganese in several Standard Reference Materials (alloys and steels) as well as in some environmental waters (portable and polluted), biological samples (human blood, urine and hair), soil samples, food samples (vegetables, fruits, tea, rice, wheat), fertilizer samples and pharmaceutical samples (multivitamin-mineral tablet and syrup), solution containing both manganese (II) and manganese (VII) and complex synthetic mixtures. The results of the proposed method for biological and food samples were comparable with AAS and were found to be in excellent agreement. The method has high precision and accuracy (s=±0.01 for 0.5 mg L-1).