Dual signaling of azide ions by deprotection of a dichlorofluorescein chloroacetate

We investigated the dual optical signaling of azide ions by the selective cleavage of fluorescein acetates. The chloroacetate derivative of 2′,7′-dichlorofluorescein showed prominent colorimetric and fluorogenic signaling behaviors toward azide ions in aqueous acetonitrile solution. Fluorescein analogs also showed a selective response, but the signaling speed was unfavorably slow. The detection of azide ions was not affected by the presence of commonly encountered anions. In particular, significant interference from sulfide ions in the azide-selective signaling of the probe was readily suppressed by using a Hg(II)–N,N,N′,N′-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) complex as a masking agent. The detection limit for the determination of azide ions by the chloroacetate of 2′,7′-dichlorofluorescein in 10% aqueous acetonitrile was 4.0 × 10−7 M (17 ppb). The signaling of azide ions in real samples using tap water and simulated wastewater was also tested.