University of Udine, Department of Agricultural, Food, Environmental and Animal Sciences (Di4A), Udine, Italy.
Università Politecnica delle Marche, Department of Life and Environmental Sciences, Ancona, Italy.
Anal Chim Acta. 2021 May 29;1161:338469. doi: 10.1016/j.aca.2021.338469. Epub 2021 Apr 2.
Inorganic phosphorous (as phosphate (PO), is one of the essential nutrients for all living forms, either terrestrial or marine. In oligotrophic seawaters, this macronutrient is limited (10 M) and its ratio with other elements (nitrogen or carbon) is denoting the health state of the marine environment; a small variation of its concentration can produce eutrophication. The gold standard method used for PO detection is based on colorimetric detection of phosphomolybdate. The colored complex is obtained by mixing water-soluble molybdenum salts (Mo(VI)) and reducing agents in acid media, along with the sample containing PO. Moreover, the kinetic of complex formation is slow, about 1 h is generally required for color to develop, exposing the assay to the drawbacks of interferences as those from silica. The detection is preferably performed in a controlled environment (i.e. in a laboratory) because several chemicals and steps of preparations are required as well as the optical instrumentation is not intended for in-field use. Electrochemical sensors offer portability and simplicity making them a practical option for on-site detection applications. To gain an analytical alternative in measuring low quantities of PO (10 M), and overcome some of the drawbacks of the classical approaches, we optimised a new easy way to produce a plastic electrode decorated with an alkyl Mo-polyoxometalate (MoO), that is soluble in organic solvents. This tetra-butyl-ammonium octamolybdate powder, [N (C4H9)4]4 Mo8O26, purposely synthetized was identified with FTIR, Raman, MS methods, and the electroactivity and reactivity with PO was confirmed in solution with cyclic voltammetry (CV). When the Mo-decorated electrode was in contact with PO, an electroactive phosphomolybdate aggregate formed at the electrode surface that was electrochemically detectable with square wave voltammetry (SWV). A remarkably low detection limit of 6.1 nM, to PO, as well as good stability and selectivity were obtained also in real samples. In fact, PO was measured in saline simulated and real seawater samples at nM concentrations in less than 5 min. The present investigation provides a new alternative to the current standard colorimetric methods to detect low phosphate concentrations, showing the potential to be used for monitoring nutrients in oligotrophic seawater.
无机磷（以磷酸盐 (PO) 的形式存在）是所有陆地或海洋生物的必需营养素之一。在贫营养海水中，这种大量营养素受到限制（10 μM），其与其他元素（氮或碳）的比例表示海洋环境的健康状况；其浓度的微小变化可能导致富营养化。用于检测 PO 的金标准方法基于磷钼酸盐的比色检测。在酸性介质中混合水溶性钼盐 (Mo(VI)) 和还原剂，并与含有 PO 的样品一起，即可获得有色络合物。此外，络合物的形成动力学较慢，通常需要大约 1 小时才能显色，这使得该测定法容易受到干扰，例如来自二氧化硅的干扰。由于需要多种化学物质和制备步骤，并且光学仪器不适合现场使用，因此最好在受控环境（即在实验室中）中进行检测。电化学传感器具有便携性和简单性，使其成为现场检测应用的实用选择。为了在测量低浓度 PO（10 μM）时获得分析替代方法，并克服经典方法的一些缺点，我们优化了一种新的简便方法来制备一种用烷基 Mo-多金属氧酸盐（MoO）装饰的塑料电极，该多金属氧酸盐溶于有机溶剂。这种四丁基铵八钼酸盐粉末 [N(C4H9)4]4Mo8O26 是专门合成的，通过 FTIR、Raman 和 MS 方法进行了鉴定，并通过循环伏安法 (CV) 在溶液中证实了其与 PO 的电活性和反应性。当 Mo 修饰的电极与 PO 接触时，在电极表面形成了电活性的磷钼酸盐聚集体，可通过方波伏安法 (SWV) 电化学检测到。在实际样品中还获得了对 PO 的低至 6.1 nM 的检测限、良好的稳定性和选择性。事实上，在不到 5 分钟的时间内，即可在模拟和真实海水盐度的海水样本中测量到 PO，浓度在 nM 范围内。本研究为检测低磷酸盐浓度的当前标准比色方法提供了一种新的替代方法，显示出在监测贫营养海水中的营养物质方面的应用潜力。
