Spectrofluorometric determination of vanadium based on the formation of a ternary complex between vanadium, peroxides, and 2-α-pyridylthioquinaidinamide.: Application to the determination of hydrogen peroxide and peroxy acids

A selective and sensitive method for the determination of the total amount of vanadium in nutritional and biological substrates is proposed. The method is based on the reaction of vanadium with 2-alpha-pytidylthioquinaldinamide (PTQA) in the presence of H2O2. The product of this reaction emits constant fluorescence, in a sulfuric acid environment, at 490 nm, with the exciting radiation set at 340 run. Various parameters such as acidity, flow rate, solvents, and temperature were studied. The presence of a surface-active agent was also considered in order to increase sensitivity. At the optimal conditions, a calibration curve was constructed, revealing a linear range of 2-100 mug L-1 and a detection limit as low as 0.5 mug L-1 while the RSD ranged in the area of 0.1-1.8%, depending on vanadium concentration. The method was successfully applied to the analysis of a wide variety of food samples, which are known to contribute to the dietary required amount of vanadium and to relevant biological matrixes. Reversing the conditions of the above reaction, the effect of the peroxy group on the vanadium-PTQA system was examined. The formation of a vanadyl complex was revealed which was suitable for the determination of hydrogen peroxide and peroxy acids. linear calibration curves in the range of 0.2-50 muM for H2O2 and 0.1-2 muM for a respective peroxy acid were obtained, yielding detection limits of 0.05 and 0.03 muM, respectively.