A highly sensitive and selective spectrofluorimetric method for the determination of manganese at nanotrace levels in some real, environmental, biological, soil, food and pharmaceutical samples using 2-(α-pyridyl)-thioquinaldinamide

Abstract

A very simple, ultra-sensitive and highly selective non-extractive spectrofluorimetric method is presented for the determination of manganese at nano-trace levels using 2-(α-pyridyl)-thioquinaldinamide (PTQA). PTQA has been proposed as a new analytical reagent for the direct non-extractive spectrofluorimetric determination of manganese(VII). This novel fluorimetric reagent, PTQA becomes oxidized in a slightly acidic (0.0125–0.05 M H₂SO₄) solution with manganese(VII) in absolute ethanol to produce a highly fluorescent oxidized product (λ_ex = 319 nm; λ_em = 373 nm). Constant and maximum fluorescence intensities were observed over a wide range of acidity (0.0125–0.05 M H₂SO₄) for the period between 5 min and 24 h. Linear calibration graphs were obtained for 0.01–800 μg L⁻¹ of Mn, having a detection limit of 1 ng L⁻¹; the quantification limit of the reaction system was found to be 10 ng L⁻¹ and the RSD was 0–2%. A large excess of over 60 cations, anions and complexing agents do not interfere in the determination. The developed method was successfully used in the determination of manganese in several standard reference materials (alloys, steels, hair and sediments) as well as in some environmental waters (potable and polluted), biological samples (human blood, urine and hair), soil samples, food samples (vegetables, fruits, tea, rice, and wheat), fertilizer samples and pharmaceutical samples (multivitamin-mineral tablets and syrup), solutions containing both manganese(II) and manganese(VII) speciation and complex synthetic mixtures. The results of the proposed method for assessing biological, food and vegetables samples were comparable with AAS and ICP-MS and were found to be in excellent agreement.