MODIFIED ELECTRODE FOR NO3- DETERMINATION IN SALINE WATERS BY VOLTAMMETRY METHOD

N. Smyk, B. Kopanytsa
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Abstract

A certain level of NO3- in water is necessary for the growth of algae. Most aquatic organisms can survive at relatively high nitrate levels, but concentrations higher than 0.2 mg/l cause fish diseases, eutrophication and algal bloom in aquariums. Thus, it is necessary to monitor the level of nitrates in aquarium water. When choosing the method of nitrate level analysis that will be used to develop an in-site saltwater monitor system, we should take into account several key factors, such as the threshold concentration and possible inferences, including high levels of Cl- in saltwater. Other desired criteria for the method are the need to get results in real time, low cost of production, and a way to perform the measurements in-site without the need for highly skilled personnel. The voltammetry was chosen as a method that satisfies our criteria. It is known that nitrate can be reduced quantitatively on a copper electrode. However, the copper electrode becomes poisoned after only a few minutes of use. Previous studies showed that a thin layer of copper deposited on the surface of various commonly used electrodes significantly improve the perfomance of the sensing system. This paper describes the fabrication process of voltammetric sensor and shows the advantage of using a glassy carbon electrode modified with electrodeposited copper layer to measure the concentration of nitrate in sea water. We have found that the modified sensor can be effectively used to catalyze nitrate reduction with a welldefined reduction wave with E= -1.1 V. We performed the cyclic voltammetric (CV) experiments and chose an optimal supporting electrolyte and the optimal conditions for the pretreatment. It was found that the peak current of nitrate increases with the increase of Cl- concentration and is stable in the range (2–3)⋅10-1 mol/l. The pH value from 3.5 to 6.0 does not influence the reaction on an electrode. The developed sensor was used to direct determine of nitrate in artificial seawater without of any sample preparation. Potentiometry with standard proсedure of Cl- precipitation was used to validate all the results. The values obtained by both methods were in good agreement with each other.
伏安法测定咸水中no3 -的改进电极
水中一定水平的NO3-是藻类生长所必需的。大多数水生生物可以在相对较高的硝酸盐水平下生存,但浓度高于0.2 mg/l会导致鱼类疾病、富营养化和水族箱中的藻华。因此,有必要监测水族馆水中硝酸盐的水平。在选择将用于开发现场盐水监测系统的硝酸盐水平分析方法时,我们应该考虑几个关键因素,如阈值浓度和可能的推断,包括高水平的Cl-在盐水中。该方法的其他期望标准是需要实时获得结果,低生产成本,以及在不需要高技能人员的情况下进行现场测量的方法。选择伏安法作为满足我们标准的方法。在铜电极上可以定量地还原硝酸盐。然而,铜电极在使用几分钟后就会中毒。以往的研究表明,在各种常用电极表面沉积一层薄的铜可以显著提高传感系统的性能。本文介绍了伏安传感器的制作过程,并介绍了用电镀铜层修饰的玻碳电极测量海水中硝酸盐浓度的优点。我们发现改进后的传感器可以有效地用于催化硝酸还原,还原波定义明确,E= -1.1 V。我们进行了循环伏安(CV)实验,选择了最佳的载体电解质和最佳的预处理条件。结果表明,硝酸盐的峰值电流随Cl-浓度的增加而增大,稳定在(2-3)⋅10-1 mol/l范围内。pH值在3.5 ~ 6.0之间不影响电极上的反应。该传感器可用于人工海水中硝酸盐的直接测定,无需任何样品制备。用氯化钠沉淀标准程序电位滴定法对所有结果进行验证。两种方法得到的数值吻合较好。
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