Signal enhancement of cetyltrimethylammonium bromide as a highly-sensitive sensing strategy for tetrabromobisphenol A

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Abstract

It is quite important to monitor tetrabromobisphenol A (TBBPA) in environmental samples due to its wide existence and high toxicity. Herein, a highly-sensitive electrochemical method was developed for the determination of TBBPA based on the strong signal enhancement effects of cetyltrimethylammonium bromide (CTAB). In pH 7.5 phosphate buffer, an irreversible oxidation peak with low height is observed for TBBPA on the surface of a carbon paste electrode (CPE), and the oxidation wave is improved greatly after addition of a low concentration of CTAB. The great peak current enlargements indicate that CTAB exhibits remarkable enhancement effects toward TBBPA oxidation. The enhancement mechanism of CTAB was investigated using electrochemical impedance spectroscopy and chronocoulometry. It is found that the existence of CTAB obviously increases the accumulation efficiency of TBBPA and facilitates its electron transfer. The linear range of this new sensing system is from 2.5 to 800 nM, and the detection limit is 0.99 nM. It was used in water sample analysis, and the recovery value was over the range from 95.74% to 102.6%.

Introduction

Tetrabromobisphenol A (TBBPA) is the highest-volume brominated flame retardant (BFR) in the world representing about 60% of the total BFR market [1]. The global consumption of TBBPA has increased from 64,000 t in 1994 to 119,700 t in 2001 [2]. In China, the TBBPA production capacity is about 18,000 t in 2007 [3]. Currently, TBBPA has attracted much attention due to the adverse health effects such as endocrine disrupting behaviors [4], [5], [6], immunotoxicity [7], [8] and neurotoxicity [9], [10]. Therefore, it is quite important to develop sensitive, simple and accurate determination methods for TBBPA.

Electrochemical determination has obtained increasing attention in environmental monitoring because it is superior in terms of speediness, handling convenience, low cost, in situ monitoring and miniaturization. However, the electrochemical studies about direct determination of TBBPA are very limited. Surfactants with amphiphilic structure have been extensively used in the field of electrochemistry for various purposes. It has been proved that the assembly of surfactants on the electrode surface has big impacts on the structure of the electrode interface, and then heavily affects the electrochemical processes of species [11], [12], [13]. Until now, cetyltrimethylammonium bromide (CTAB), a typical cationic surfactant, has been successfully employed to improve the response signals of estrogens [14], nitrophenol isomers [15], bisphenol A [16] and ciprofloxacin [17].

The main objective of this work is to develop a simple, sensitive and accurate method for the determination of TBBPA utilizing the excellent enhancement effects of CTAB. On the surface of a carbon paste electrode (CPE), the oxidation activity of TBPPA is very low, and the resulting oxidation signals are also weak. However, the oxidation wave of TBBPA on the CPE surface is improved significantly after addition of CTAB. The existence of CTAB enhances the electron transfer ability and the surface accumulation efficiency of TBBPA, showing strong signal amplification ability. As a result, the oxidation signals and detection sensitivity of TBBPA are improved greatly.

Section snippets

Reagents

All chemicals were of analytical grade and used as received. 0.01 M stock solution of TBBPA (Laboratories of Dr. Ehrenstorfer, German) was prepared using ethanol, and stored at 4 °C. Cetyltrimethylammonium bromide (CTAB), graphite powder (spectral reagent) and paraffin oil were purchased from Sinopharm Chemical Reagent Company (Shanghai, China). Ultrapure water was obtained from a Milli-Q water purification system and used throughout.

Instruments

Electrochemical measurements were carried out on a CHI 660C

Electrochemical behaviors of TBBPA

The electrochemical behaviors of TBBPA in 0.1 M phosphate buffer solutions with different pH values were studied using cyclic voltammetry (CV). As shown in Fig. 1A, a pH-dependent oxidation wave is observed for TBBPA, and it moves negatively when improving the pH value from 6.0 to 8.0, indicating that protons are involved in the oxidation process. Moreover, a good linear relationship is observed for the oxidation peak potential (Ep) of TBBPA and the pH values, as confirmed from Fig. 1B. The

Conclusions

A simple strategy for sensitive determination of TBBPA has been developed based on the enhancement effects of CTAB. The assembly of CTAB on the CPE surface improves the electron transfer ability and accumulation efficiency of TBBPA. So the oxidation signals and detection sensitivity of TBBPA are improved greatly in the presence of CTAB. The detection limit is at the nM level, and the practical applications in water samples reveal good accuracy.

Acknowledgements

This work was supported by the National Basic Research Program of China (973 Program, No. 2015CB352100) and the Jiangxi Province Foreign Cooperation Projects (No. 20141BDH80028).

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