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 H2O-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 1H NMR titrations that indicate deprotonation of OH and NH moieties by these ions. 27Al 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.