2-(α-Pyridyl)-thioquinaldinamide (PTQA)-A novel fluorimetric reagent in inorganic trace analysis. I: The nonextractive,nonquenching fluorescent method for the determination of chromium(VI)

A direct fluorimetric method for determining Cr(VI) in aqueous solutions is described. The nonfluorescent reagent 2-(-pyridyl)-thioquinaldinamide (PTQA) and Cr(VI) interact to produce an intensely fluorescent species _ex(max) 360 nm; _em(max) 500 nm] showing constant and maximum fluorescence intensity in slightly acidic media (0.18N–1.08N H₂SO₄). The fluorescence attains its maximum value within 5 min and remains unchanged for 24 h. The system obeys Beer's law from 2 ng/ml to 0.8 g/ml of Cr(VI). Over sixty cations, anions and complexing agents are without any effect on the fluorimetric determination of 0.1 g/ml of Cr(VI). The method has been tested with synthetic mixtures, steels, solutions containing both Cr(III) and Cr(VI), and environmental samples.