A selective fluorescence quenching method for the determination of trace hypochlorite in water samples with nile blue A

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Highlights

  • The method exhibited highly selective and real time.

  • ClO could be detected at low micromolar levels and in water samples.

  • Fluorescence quenching mechanism was discussed.

Abstract

Recently, growing concern has been paid to the sensitive and selective determination hypochlorite because of its crucial roles in our daily life. In this paper, a simple, sensitive, selective spectrofluorimetric method was applied to detect the hypochlorite. Upon reaction of the probe with ClO, a fluorescence quenching was observed. The method was shown to be highly selective for ClO, and exhibited real time response as well as linear relationship to ClO concentration, and hypochlorite could be detected at low micromolar levels in aqueous solution. The linear response range of hypochlorite (R2 = 0.9994) was from 0.13 to 25 µmol/L. The detection limit (3σ/k) was 0.04 µmol/L, which was lower than that of previously mentioned. The accuracy and reliability of the method was further ensured by recovery studies via a standard-addition method, with percentage recoveries in the ranges of 95.0–104.8%, 96.3–102.6% and 97.8–102.5, respectively. Additionally, the quenching mechanism was discussed. Judging from temperature, fluorescence lifetime, UV–visible absorbance spectra, quenching mechanism was proved static quenching. This method was finally used to detect the hypochlorite in local water samples.

Introduction

Sodium hypochlorite is the most important commonly used chlorinated substance and extensively used as a household cleaning agent. Also, it is widely used in textile industry as a bleaching agent and disinfectant in fabrics, wood pulp food, milk industries and treatments including drinking water, swimming pool water, treated wastewater for non-potable reuse [1]. Normally, hypochlorite is handled as concentrated aqueous solutions, typically, in the concentration range of 10−5 to 10−2 mol/L [2], [3], which is a potential health hazard to human and animal [4], [5]. Thus, it is necessary to develop a rapid and sensitive method for assay hypochlorite. With the growing concern about drinking water safety, the environment water can be of an interest research filed.

A number of methods which detect hypochlorite, colorimetric, luminescent, electrochemical and chromatographic have been reported. As well known, owing to their high sensitivity and selectivity, fluorescence techniques have been widely used for rapid determination of various analytes [6]. Recently, some recent probes have been developed for hypochlorite based on its strong oxidation properties [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17]. For example, dibenzoylhydrozine to dibenzoyl diimide [7], oxidation reactions of thiol to sulfonate derivative [8], p-methoxyphenol to benzoquinone [9], hydrazone to aldehyde [18], and oxidation of p-alkoxyaniline [19]. In addition, rhodamine and fluorescein-based fluorescent probes have been reported for HClO [8], [20]. Chen et al. developed two fluorescent probes for detection HClO which functioned in an organic co-solvent system [21]. These probes, however, not only have complicated structures, but also are not easily synthesized.

Based on the strong oxidation of hypochlorite, in this paper, a conventional ClO specific fluorescence probe based on the commercial available reagent nile blue A (Scheme 1) which has high sensitivity and selectivity toward ClO was reported. Also, its stability was shown over other reactive oxygen and/or nitrogen species in BR buffer solution.

Section snippets

Apparatus

All the fluorescence measurements were carried out a Hitachi 2500 spectrofluorophotometer (Tokyo, Japan), at 634 nm using 1 cm path length. Absorption spectra were recorded on a UV-8500 spectrometer (Tianmei, Shanghai, China). The pH values were measured by a pH-3D pH meter (Shanghai Scientific Instruments Company, China).

Reagents

The stock solution of sodium hypochlorite (NaClO), nile blue A (NBA), Triton X-100 were 1.0 × 10−4 mol/L, 1.0 × 10−4 mol/L, 3.0% (w/v), respectively. The stock solution was

Fluorescence spectra

Fig. 1 showed the change in the fluorescence spectra when the various concentrations of ClO were added to the BR buffer solution (pH 2.0), containing probe NBA (10.0 µmol/L) (λex = 634 nm). The fluorescence intensity of 686 nm was gradually decreased with the addition of ClO. Upon addition of ClO to the NBA with BR buffer solution, the visual color change (blue to light blue) was observed.

Effects of NBA concentration

The influence of NBA concentration in the presence of Triton X-100 and hypochlorite on the emission

Conclusions

In summary, we reported a simple, cost-effective, highly selective spectrofluorimetric method for ClO, which avoided complicated synthesis. In this work, the probe, on one hand, exhibited well selective compared with other oxidative ions; on the other hand, showed the stability for other common ions. Also, the well linear relationship fluorescence intensity between hypochlorite was obtained under realistic condition. All these selective and sensitive results indicated that the probe could meet

Acknowledgments

The authors gratefully acknowledge financial support for this study by grants of the National Natural Science Foundation of China (Grant no. 21175109), the Special Fund of Chongqing Key Laboratory (CSTC) and the Fundamental Research Funds for the Central Universities (XDJK2013A022).

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