Advances in Analytical Chemistry
Vol.05 No.04(2015), Article ID:16339,8 pages
10.12677/AAC.2015.54006

Determination of Bisphenol A in Polycarbonate Plastic Products Using Single-Walled Carbon Nanotubes Modified Glassy Carbon Electrode

Zhiling Feng, Qing Liu, Shishi Feng, Yingying Lin, Sisi Lin, Xuexiang Weng*

Department of Chemistry and Life Sciences, Zhejiang Normal University, Jinhua Zhejiang

Received: Oct. 15th, 2015; accepted: Nov. 9th, 2015; published: Nov. 13th, 2015

Copyright © 2015 by authors and Hans Publishers Inc.

This work is licensed under the Creative Commons Attribution International License (CC BY).

http://creativecommons.org/licenses/by/4.0/

ABSTRACT

Direct electrochemistry of bisphenol A (BPA) at the single-walled carbon nanotubes (SWNTs) modified glassy carbon electrode (GCE) is studied in this paper. The experimental results show that the electrochemical behavior of BPA on carbon nanotubes modified electrode is an irreversible electrochemical oxidation process controlled by adsorption in phosphate buffer solution (pH 8.0). Under the optimised experimental conditions, the proposed biosensor exhibits a wide linear range of 0.04 - 8 μM with a low detection limit of 23 nM. This method is simple, fast and suitable for analysis of BPA in polycarbonate products.

Keywords:Bisphenol A, Single-Walled Carbon Nanotubes, Cyclic Voltammetry (CV)

单壁碳纳米管修饰电极测定聚碳酸酯塑料中的双酚A

冯志玲,刘青,冯施施,林莹莹,林思思,翁雪香*

浙江师范大学化学与生命科学学院,浙江 金华

收稿日期:2015年10月15日;录用日期:2015年11月9日;发布日期:2015年11月13日

摘 要

用循环伏安法(CV)研究了环境激素双酚A (BPA)在单壁碳纳米管(SWNTs)修饰电极上的电化学行为。实验结果表明,在pH = 8.0的磷酸盐缓冲溶液中,BPA在碳纳米管修饰电极上的电化学行为是受吸附控制的不可逆电化学氧化过程。在优选的实验条件下,峰电流与BPA浓度在0.04~8 μM范围内呈良好的线性关系,其中检测限为23 nM (3倍信噪比)。该方法简单,快速,灵敏,可用于矿泉水瓶等塑料制品中BPA的检测。

关键词 :双酚A,单壁碳纳米管,循环伏安法

1. 引言

双酚A (Bisphenol A, BPA)是一种重要的有机化工原料,由于它能使聚碳酸酯等塑料产品变得透明、耐用、防摔等特点而被广泛用于生产婴儿奶瓶、太空杯、矿泉水瓶、塑料餐具等[1] -[3] 。近年来,有研究表明,BPA是一种具有弱雌激素活性的环境内分泌干扰素,具有模拟雌性激素的作用,即使少量存在也能使动物产生雌性早熟、精子数下降、前列腺增生等疾病且对胎儿及婴幼儿的影响更为明显[4] 。目前,我国、美国、欧洲及加拿大等国家已逐步禁止了在食品包装或容器中使用BPA。因此,建立一种快速、灵敏、简便、准确的BPA痕量快速检测技术具有重要意义。目前,已报道的BPA的分析测试方法,主要有分光光度法[5] [6] 、色谱法[7] -[10] 、荧光法[11] -[13] 、酶联免疫吸附法[14] [15] 和电化学方法[16] -[18] 等。其中电化学检测法由于其灵敏度高,简单、快速且易于微型化从而实现实时、现场检测而备受关注。

为了进一步提高电化学检测的灵敏度,在检测电极上修饰电催化性能优异的纳米材料是首选。碳纳米管自1991年被发现以来,由于其比表面积大,电子传递能力强,响应时间快而且电极产物污染小等优点,在过去的25年里已成为传感器领域的领军材料[19] -[21] 。碳纳米管可分为单壁碳纳米管(SWNTs) 和多壁碳纳米管(MWNTs)两类。目前已有关于MWNT用于BPA检测的报道[22] [23] 。

本文建立了SWNT修饰电极检测 BPA的电化学方法,并探讨了BPA在修饰电极上的氧化机理及相关动力学行为。在最优化的实验条件下,对聚碳酸酯塑料制品中的双酚A进行了检测,取得了令人满意的结果。

2. 实验部分

2.1. 仪器与试剂

CHI660C 电化学工作站(上海辰华仪器公司);电化学实验用三电极系统:碳纳米管修饰电极为工作电极,铂丝电极为对电极,饱和甘汞电极(SCE)为参比电极;pHS-4CT 型精密酸度计(上海大普仪器有限公司);BSA224S电子天平(赛多利斯科学仪器(北京)有限公司);SB-3200DTD超声波清洗仪(宁波新芝生物科技股份有限公司);微量进样器;可调微量锁紧移液器。

SWNTs购自深圳纳米港有限公司(直径约1 nm),BPA购于上海生工生物公司,配置成0.2 mol∙L−1的乙醇标准溶液备用。N,N-二甲基甲酰胺(DMF)购自上海菲达工贸有限公司,其余试剂均为分析纯以上,所有电化学实验都在室温下进行。

2.2. 修饰电极的制备

将玻碳电极(GCE)分别用粒径为0.3 μm和0.05 μm的Al2O3抛光粉抛光成镜面,并依次用二次蒸馏水、无水乙醇和二次蒸馏水超声清洗3 min左右,取出后在室温下自然晾干,备用。取一定量的SWNTs固体用DMF溶剂超声分散2 h。混合均匀后,滴5 μL至抛光好的玻碳电极表面,阴凉干燥处自然风干即得所需的修饰电极(SWNTs/GCE)。

2.3. 试验方法

在0.1 mol∙L−1 Na2HPO4和NaH2PO4缓冲溶液(PBS)中,插入三电极体系,用循环伏安法考察不同pH值、不同扫描速率下,BPA在SWNTs/GCE上的电化学响应。

2.4. 实际样品提取

将当地超市购得的矿泉水瓶和食品包装袋剪碎,各称取2 g左右的样品于烧杯中,加入30 mL去离子水,超声溶解30 min后于70℃中加热48 h,过滤,收集滤液,样品重复收集2次,定容至100 mL待测。

3. 结果与讨论

3.1. BPA在碳纳米管修饰电极上的电化学行为

图1是扫描电位范围为0.1~0.8 V时,在0.1 M的磷酸盐(pH = 8.0)缓冲溶液中,6 μM的BPA在GCE (曲线b)和SWNTs/GCE上(曲线c)的循环伏安响应。由图可知,BPA在电极上的氧化是一个完全不可逆的过程,其氧化峰电位由裸玻碳电极上的0.51 V负移至碳纳米管修饰电极上的0.44 V,而且在碳纳米管修饰电极上,峰电流显著增加,这说明了碳纳米管修饰电极对BPA有较好的电催化作用。这种催化作用可归因于:一方面,碳纳米管比表面积大,导致BPA在电极表面的富集量明显增加,从而使峰电流增大;另一方面,由于碳纳米管具有良好的导电能力,使电子转移速率加快,因而BPA的氧化过电位得以降低。

3.2. 电解液及相应pH的选择

为了考察不同的缓冲体系对BPA催化氧化的影响,我们选用了三种常用缓冲溶液作为考察对象,分别是邻苯二甲酸-盐酸缓冲溶液(pH 2.2~3.8),乙酸-乙酸钠缓冲液(pH 2.6~5.8)和磷酸氢二钠-磷酸二氢钠缓冲液(pH 3.8~10.2)。实验结果发现BPA在pH较高的PBS体系中的响应灵敏度高且峰形好。通过比较BPA在不同pH值的PBS溶液中的循环伏安曲线(图2)可知:pH值在3.8~10.2范围内变化时,氧化峰电位随着溶液 pH 的增加而负移,说明BPA在碱性介质中更容易发生氧化反应。而且,BPA在pH = 8.0的缓冲溶液中的氧化峰电流相对最大。因此,实验选择pH 8.0的磷酸盐缓冲溶液为最佳支持电解质。

此外,氧化峰电位与pH值呈线性关系(图3),线性方程为,这表明BPA的氧化过程是和H+有关的,从直线的斜率−0.0599 mV/pH可知,此氧化过程中质子转移数和电子转移数相等。

3.3. 峰电流与扫描速度的关系及BPA氧化机理的考察

电位扫描速度也对BPA在修饰电极上的循环伏安行为也有较大影响。在pH 8.0的磷酸盐缓冲溶液中,扫速越高,氧化峰电流越大。扫描速率从20~500 mV范围内变化时,BPA的氧化峰电流与扫描速率呈良

Figure 1. Cyclic voltammograms obtained at bare GCE (curve b) and SWNTs/GCE (curve c) in 0.1 mol∙L−1 PBS (pH 8.0) with 6 μM BPA. Curve a is cyclic voltammogram of GCE in blank PBS. Scan rate: 50 mV∙s−1

图1. 6 μM的BPA在GCE (曲线b)和SWNTs/GCE上(曲线c)的CV图;曲线a为GCE在空白PBS (0.1 mol∙L−1, pH = 8.0)中的CV图

Figure 2. Cyclic voltammograms of 10 μM BPA at SWNT/ GCE in 0.1 mol∙L−1 PBS with different pH (a) pH = 3.8, (b) pH = 5.5, (c) pH = 6.2, (d) pH = 6.9, (e) pH = 7.4, (f) pH = 8.0, (g) pH = 10.2; Scan rate: 50 mV∙s−1

图2. 不同pH值PBS溶液中,10 μMBPA溶液在SWNT/ GCE上的CV图,(a) pH = 3.8;(b) pH =5.5;(c) pH = 6.2;(d) pH = 6.9;(e) pH = 7.4;(f) pH = 8.0;(g) pH = 10.2

好的线性关系(图4(b)),这说明BPA的氧化过程是一个吸附控制的过程[24] [25] 。由于BPA溶液的氧化是一个不可逆的吸附控制的过程,所以氧化峰电位和扫描速度应该满足Laviron方程[26] [27] :

(1)

其中,α是电子转移系数,无量纲,对于完全不可逆的电极过程,α取0.5;ks是表面反应速率常数,s−1;R是气体常数,8.314 J/(K·mol);T为温度,本方法中均取298 K;F是法拉第常数,取96,480 C/mol;ν是扫描速度,mV/s;E0是标准电位V。由图4(a)可知,在扫描速率范围20~500 mV/s内与lnν的线性方

Figure 3. Calibration curve of Epa to pH

图3. 氧化峰电位Epa与pH值的关系图

(a) (b)

Figure 4. Effect of pH on the oxidation current (a), oxidation potential (b) on the response to 4 × 10−4 mol∙L−1 BPA

图4. 不同扫速时40 μM的BPA溶液的(a)氧化峰电流(b)氧化峰电位与扫描速率之间的线性关系图,扫速范围为20,50,100,200,300,500 mV/s

程为:,该式结合Laviron方程可计算得n约等于2。这个结果意味着BPA在碳纳米管电极表面的电化学氧化过程涉及2个电子和2个质子的过程,这与文献的研究结果相符[28] 。

3.4. 线性范围与检出限

在优化的实验条件下,微分脉冲伏安法(DPV)显示,峰电流随着BPA浓度的增大而增大,二者的关系如图5所示。在0.04~8 μM范围内浓度与峰电流呈良好的线性关系,其线性回归方程为:,其中,检测限为23 nM (3倍信噪比)。

Figure 5. DPVs of BPA at various concentration in PBS (pH = 8.0)

图5. 不同浓度的BPA在PBS 8.0中的DPV图,内插图为浓度与峰电流的线性拟合图

Table 1. Determination of BPA in the spiked plastic products samples

表1. 在塑料制品的容器中检测BPA的加标回收率

Recovery = (Found – Measured)/Added × 100%.

3.5. 共存离子的影响

实验结果表明,在优化的体系中,研究了一些常见无机盐离子及有机化合物对BPA的影响。当BPA的含量为5 × 10−6 M,其无机盐离子:K+,Ca2+,Na+,Mg2+,Al3+,Zn2+,Cu2+及有机化合物:甲醇,乙醇,苯酚其浓度为5 × 10−6时,对BPA的测定几乎无干扰(其误差小于5%)。

3.6. 实际样品的检测

为了验证该电极的实际检测能力,我们采用标准加入法测试了几个不同品牌矿泉水瓶中的BPA含量。实验结果如表1所示,不同样品中的加标回收率为96.0.3%~106.3%,表明该方法可用于实际样品的检测。

4. 结论

本文用涂层法制备了SWNT修饰电极,并考察了该电极对BPA的电化学氧化机理及动力学过程。同时,构建了该修饰电极检测聚碳酸酯塑料制品中BPA的方法,实验结果令人满意。

致谢

感谢浙江省自然科学基金(LQ12B05002)和科学基金会的资助。

文章引用

冯志玲,刘 青,冯施施,林莹莹,林思思,翁雪香. 单壁碳纳米管修饰电极测定聚碳酸酯塑料中的双酚A
Determination of Bisphenol A in Polycarbonate Plastic Products Using Single-Walled Carbon Nanotubes Modified Glassy Carbon Electrode[J]. 分析化学进展, 2015, 05(04): 49-56. http://dx.doi.org/10.12677/AAC.2015.54006

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