Department of Chemistry, Graduate School of Natural Science and Technology, Okayama University, Okayama, Japan.
Department of Chemistry, Graduate School of Natural Science and Technology, Okayama University, Okayama, Japan.
Anal Chim Acta. 2020 Oct 23;1135:99-106. doi: 10.1016/j.aca.2020.08.051. Epub 2020 Aug 27.
This work describes a methodology that can be used to achieve on-site analysis of paraquat in water samples by using a miniaturized portable photometer consisting of a couple of light-emitting diodes (LEDs). Paraquat produces a colored radical via a redox reaction with sodium dithionite, which is unstable against oxygen in solution. The steps taken to stabilize the reagent solution included control of the pH and the addition of organic solvents, but the most effective was the formation of an oil layer. Together, these steps stabilized the reagent solution for two days. An increase in the duration of reagent stability, however, is necessary in order to transport the reagent for on-site applications in remote locales. For the time being, an excess amount of solid sodium dithionite can be added directly to sample solutions because the unreacted dithionite shows no influence on absorbance of the paraquat radical. Orange LEDs with a maximum emission wavelength of 609 nm were employed in the portable photometer to measure the absorbance of paraquat radical produced by a redox reaction that has an absorption maximum of 603 nm. The developed photometer showed excellent performance with a linear range of from 2.0 mg L to 40.0 mg L and a linear regression (r = 1). The limits of detection and quantification were 0.5 mg L and 1.5 mg L, respectively, intra-day precision (n = 3) and inter-day precision (n = 5) were both less than 5%, and accuracy based on the percentage of sample recovery ranged from 89 ± 0 to 105 ± 0% (n = 3). The proposed method was applied to the analysis of paraquat in water samples taken from rice fields. The results showed no paraquat in all thirteen samples, which could have been due to strong adsorption of paraquat by soil particles and/or to complications with the sampling conditions. To confirm the adsorption onto soil of paraquat contained in water, we constructed an artificial rice field where water containing paraquat was impounded above the soil layer. The results showed that paraquat in water gradually decreased within three days and could be measured in the soil on the fourth day. These results were confirmed by HPLC analysis, which underscores the utility of this portable photometer for the on-site monitoring of paraquat in water samples.
本工作描述了一种方法，可利用由一对发光二极管（LED）组成的小型便携式光度计在现场分析水样中的百草枯。百草枯通过与连二亚硫酸钠的氧化还原反应产生有色自由基，但该自由基在溶液中不稳定，易受氧气影响。为稳定试剂溶液采取了一些措施，包括控制 pH 值和添加有机溶剂，但最有效的方法是形成油层。这些步骤共同使试剂溶液稳定了两天。然而，为了将试剂运输到偏远地区进行现场应用，需要延长试剂的稳定性持续时间。目前，可以直接向样品溶液中添加过量的固体连二亚硫酸钠，因为未反应的连二亚硫酸钠对百草枯自由基的吸光度没有影响。便携式光度计中使用了最大发射波长为 609nm 的橙色 LED 来测量氧化还原反应产生的百草枯自由基的吸光度，该反应的吸收最大值为 603nm。开发的光度计表现出出色的性能，线性范围为 2.0mg/L 至 40.0mg/L，线性回归（r=1）。检测限和定量限分别为 0.5mg/L 和 1.5mg/L，日内精密度（n=3）和日间精密度（n=5）均小于 5%，基于样品回收率的准确度范围为 89±0%至 105±0%（n=3）。该方法应用于从稻田采集的水样中百草枯的分析。结果表明，所有 13 个样品中均未检出百草枯，这可能是由于土壤颗粒对百草枯的强烈吸附和/或采样条件复杂所致。为了确认水中百草枯吸附到土壤上，我们构建了一个人工稻田，将含有百草枯的水蓄在土壤层上方。结果表明，水中的百草枯在三天内逐渐减少，第四天可以在土壤中测量到。高效液相色谱分析证实了这些结果，突出了这种便携式光度计在现场监测水样中百草枯的实用性。
