Colorimetric recognition of hydrazine in aqueous solution by a bromophenol blue-tethered ion-pair-like ratiometric probe

Hydrazine or hydrazine hydrate (N2H4·H2O) is a potential neurotoxin and has several mutagenic effects in physiological systems. Therefore, the development of synthetic organic probes that are sensitive and selective to hydrazine is of tremendous importance. Unfortunately, however, the hydrazine-selective sensing probes that rely upon minimum usage of the organic solvents (≤5%, v/v) are still rarer. In this work, an ion-pair-like mono acetate derivative of bromophenol blue has been developed as a fairly selective ratiometric probe for the naked-eye recognition of hydrazine in a solution of tris buffer and EtOH (19:1, v/v) at physiological pH. The chromogenic signalling relies upon hydrazine-induced cleavage of an ester moiety of the probe to its resonance stabilized quinonoid form, resulting in momentous variations in its spectrophotometric profile. Meanwhile, the colour of the probe solution changed from mustard yellow to blue within few minutes. This sensing assay could be successfully applied in the recognition of hydrazine in real environmental and pharmaceutical samples with satisfactory recoveries. Given the cost-effectiveness, simplicity and versatility, for instance, direct analysis of colorimetric probes, it is reasonable to propose that the present method can serve as a complementary method for prompt inspection of hydrazine in boiler feed water.