3-Hydroxy-2-naphthoic hydrazide as a probe for fluorescent detection of cyanide and aluminium ions in organic and aquo-organic media and its application in food and pharmaceutical samples.

The commercially available fluorophore, 3-hydroxy-2-naphthoic hydrazide (RS2), has rationally been selected for the study, which displays a rapid fluorescent response and high sensitivity for CN and Al(III) ions in neat DMSO and HO-DMSO (1:1 v/v) media. The addition of CN to RS2 triggers an enhancement in fluorescence at 505 nm (green fluorescence), while the addition of Al(III) increases the fluorescence of the probe with a blue-shift of emission maximum by 25 nm (bluish-green fluorescence). The probe's action was investigated by H NMR titrations that indicate deprotonation of OH and NH moieties by these ions. Al NMR of RS2-Al(III) complex suggests an octahedral geometry for the complex. The sensitivity of the fluorescent-based assays in aq. DMSO medium, 0.8 µM for CN and 1.9 µM for Al(III) ions are far below the limits in the World Health Organization guidelines for drinking water. RS2 detects Al(III) by the chelation-enhanced fluorescence (CHEF) mechanism. Besides, RS2 was successfully applied to detect CN and Al(III) ions in food materials and pharmaceutical samples, respectively.