Universidad de la República, Facultad de Química, Group for Instrumentation and Automation in Analytical Chemistry (GIAQA), Av. Gral. Flores 2124, 11800, Montevideo, Uruguay.
Universidad de la República, Facultad de Química, Group for Instrumentation and Automation in Analytical Chemistry (GIAQA), Av. Gral. Flores 2124, 11800, Montevideo, Uruguay.
Talanta. 2020 Mar 1;209:120589. doi: 10.1016/j.talanta.2019.120589. Epub 2019 Nov 23.
The molybdenum blue method using antimony and ascorbic acid was studied for the determination of phosphorus (as orthophosphate) by means of sequential injection analysis (SIA). In order to avoid the interference of the Schlieren effect in the photometric measurements a stopped-flow kinetic approach was adopted monitoring the absorbance of the reaction bolus inside the flow cell. Aiming at enhancing the sensitivity of the method, the effect of the order of addition of the reactants was studied. It was found that the best sensitivity was attained by adding separate reagents and acidifying only after the phosphate, molybdate and antimony solutions were already mixed; the reductant (ascorbic acid) was then added. In this way a sensitivity enhancement in excess of 10 times was obtained when compared to the addition of the phosphate solution to the acidified mixture of molybdate and antimony. It is proposed that the difference in sensitivities could be explained by the existence of different mechanisms for the formation of the intermediate phosphoantimonyl molybdic acid (PMA). Thus the selected sequence in the order of addition, where sulphuric acid is added to the mixture of the other reactants would lead to higher production of PMA in turn conducting to a faster reduction reaction. The resulting SIA method was validated finding limits of detection (3s/m) and quantification (10s/m) of 0.0077 and 0.026 mg-P L respectively. Linearity was confirmed in the range up to 2 mg-P L. Precisions (s, n = 10) were in the range 1.8%-4.0%. 32 water samples of different types and origins were analysed by the proposed method and by ion chromatography, obtaining a regression curve y = 0.990× - 0.0019, with a determination coefficient R = 0.973.
钼蓝法使用锑和抗坏血酸通过顺序注射分析（SIA）测定磷（正磷酸盐）。为了避免在光度测量中出现慧差干扰，采用停流动力学方法，在流池内监测反应液的吸光度。为了提高方法的灵敏度，研究了反应物添加顺序的影响。结果发现，通过分别添加试剂并在磷酸盐、钼酸盐和锑溶液混合后酸化，然后添加还原剂（抗坏血酸），可以获得最佳的灵敏度。与将磷酸盐溶液加入酸化的钼酸盐和锑混合物相比，灵敏度提高了 10 倍以上。提出的差异灵敏度可以通过形成中间磷锑钼酸（PMA）的不同机制来解释。因此，在所选择的添加顺序中，先将硫酸加入到其他反应物的混合物中，会导致 PMA 的产量更高，从而导致更快的还原反应。所得到的 SIA 方法经过验证，检测限（3s/m）和定量限（10s/m）分别为 0.0077 和 0.026mg-P/L。在线性范围内可达到 2mg-P/L。精密度（s，n=10）在 1.8%-4.0%之间。用所提议的方法和离子色谱法分析了 32 种不同类型和来源的水样，得到回归曲线 y=0.990×-0.0019，决定系数 R=0.973。
