一种基于电化学还原醌的测定铵盐和甲醛含量的新方法

发布时间：2018-05-02 08:05

本文选题：对苯醌 + 弱酸　；参考：《辽宁大学》2017年硕士论文

【摘要】：随着全球经济发展进入新常态,人类向自然界索取的越来越多,由之而产生的环境问题也越来越多,其中以空气污染与水体污染最为严重。人类迫切需要一种能够快速检测空气及水体中污染物的方法,本论文建立了一种快速有效地检测空气中甲醛含量及水体中铵盐含量的新方法。具体方法是利用电化学方法,通过对比对苯醌(Q)还原过程中,铵盐和甲醛反应所生成酸提供质子,产生新峰的峰电流高度来检测铵盐和甲醛含量。实验中由于甲醛和NH4+酸性都非常弱,不能释放足够的质子来抑制电极界面pH的升高,所以我们通过铵盐与甲醛作用(甲醛法)定量生成相对较强的酸,从而抑制电极表面pH的上升,产生新的差分脉冲峰,该峰不受对苯醌、铵盐和甲醛浓度的影响,只随生成酸浓度的增加而升高,这样可以更快更准确的测定其含量。根据实际实验情况我们首先采用循环伏安法验证此方法的可行性,接下来用差分脉冲法进行测定。由实验结论可知,当水溶液中有质子存在时,对苯醌在水溶液中还原时首先接受游离态的质子,反之对苯二酚在氧化时会释放质子。在非缓冲的水溶液中,它们的氧化还原结果会使电极表面的pH值升高或降低。酸释放的质子会导致在相对较正的电位上产生新的还原峰。此外,不同pKa的酸,由于其释放质子的能力不同,从而导致新峰的出峰电位也不同,所以可以根据酸的出峰电位来判断物质的酸性强弱。因在中性条件下,乙酸铵和甲醛均不能提供质子导致新峰的产生,所以我们利用甲醛法作用的产物—较强酸为对苯醌还原提供质子。本论文根据以上原理,通过测定水溶液中生成酸含量从而定量测定了铵盐及甲醛含量。由实验数据可知,生成酸浓度决定对应较正电位的峰电流值,我们可以根据酸浓度与峰电流绘制标准曲线,从而可得出铵盐和甲醛的浓度,我们还可以用此方法来测定未知样品中NH4+和甲醛的含量。以上测定方法较传统的测试方法不仅灵敏度提高了,且不需复杂的预处理,为实际的电化学测定铵盐和甲醛提供了一个新途径。
[Abstract]:With the development of global economy entering into the new normal, more and more human beings demand from nature, and more and more environmental problems arise from it, among which air pollution and water pollution are the most serious. There is an urgent need for a rapid method to detect pollutants in air and water. In this paper, a new method is established to detect formaldehyde in air and ammonium salt in water. The specific method is to detect the content of ammonium salt and formaldehyde by comparing the acid produced by the reaction of ammonium salt with formaldehyde and the peak current height of the new peak in the process of p-benzoquinone Q) reduction by electrochemical method. Because the acidity of formaldehyde and NH4 is so weak that we can not release enough protons to restrain the increase of pH at the electrode interface, so we quantitatively produce relatively strong acids by the interaction of ammonium salt with formaldehyde (formaldehyde method). Therefore, the increase of pH on the electrode surface is inhibited and a new differential pulse peak is produced. The peak is not affected by the concentration of p-benzoquinone, ammonium salt and formaldehyde, but only increases with the increase of the concentration of the formed acid, which can be measured more quickly and accurately. According to the actual experimental conditions, we first use cyclic voltammetry to verify the feasibility of this method, and then use differential pulse method to determine. The experimental results show that when protons exist in aqueous solution, p-benzoquinone first receives protons in the free state when it is reduced in aqueous solution, whereas hydroquinone releases protons when it is oxidized. In non-buffer aqueous solutions, their redox results increase or decrease the pH value of the electrode surface. Protons released by acids cause new peaks of reduction at relatively positive potentials. In addition, due to the different proton release ability of different pKa acids, the peak potential of the new peak is also different, so the acidity can be judged according to the acid peak potential. Under neutral conditions, ammonium acetate and formaldehyde can not provide protons to lead to new peaks, so we use the product of formaldehyde method-strong acid to provide proton for p-benzoquinone reduction. According to the above principle, the content of ammonium salt and formaldehyde in aqueous solution was determined quantitatively by the determination of the acid content in aqueous solution. According to the experimental data, we can draw the standard curve according to the acid concentration and peak current to determine the peak current value corresponding to the positive potential, and then we can get the concentration of ammonium salt and formaldehyde. We can also use this method to determine the content of NH4 and formaldehyde in unknown samples. The above methods not only improve the sensitivity, but also do not require complex pretreatment, which provides a new way for the electrochemical determination of ammonium salt and formaldehyde.
【学位授予单位】：辽宁大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：X830;O657.1

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