Dept. of Chemistry, Johns Hopkins University, Baltimore, MD, USA.
Dept. of Chemistry, Johns Hopkins University, Baltimore, MD, USA.
Talanta. 2020 Oct 1;218:121148. doi: 10.1016/j.talanta.2020.121148. Epub 2020 May 16.
Hydroxyl radicals (∙OH) are powerful oxidizing species formed naturally in the environment or artificially produced to destroy contaminants in water treatment facilities. Their short lifetime and high reactivity, however, present a significant challenge to quantifying their concentration in solution. Herein, we developed a novel method to accurately measure the steady-state ∙OH concentration and total ∙OH dose produced during the UV photolysis of hydrogen peroxide (HO) by monitoring the loss of salicylic acid (SA). This information can be acquired using only benchtop UV-Vis spectroscopy, thus expanding measurement capabilities of resource-limited laboratories by eliminating the need for sophisticated instrumentation. To improve the precision with which the rate of SA loss was measured compared to previous methods, we applied principal component analysis (PCA) to fit the UV-Vis spectra collected during SA exposure to ∙OH. For our experimental conditions consisting of 12 mL solutions composed of ≤ 100 mM HO and 0.07 mM SA, the steady-state ∙OH concentration throughout the complete photolysis of HO was 1.33 × 10 M ± 1.14 × 10 M. This represents more than a ten-fold improvement in reducing the uncertainty of the measurement, with respect to narrowing the 95 % confidence interval, compared to a previous method that employed matrix analysis to process the spectra. Furthermore, the variance of the measured ∙OH concentrations was reduced by a factor of 100 compared to previous methods. Using PCA, the limit-of-detection and limit-of-quantitation for ∙OH are 5.33 × 10 M and 1.23 × 10 M, respectively. By developing quantitative relationships among ∙OH concentration, HO concentration, and UV exposure time, we also show how to calculate the equivalent exposure to ∙OH generated in natural aquatic environments by indirect photolysis. Finally, we use this methodology to demonstrate that the presence of suspended carbonaceous nanoparticles at concentrations as high as 300 ppm does not affect ∙OH concentration.
羟基自由基（·OH）是在环境中自然形成或人工产生的强氧化性物质，用于破坏水处理设施中的污染物。然而，由于其短寿命和高反应活性，准确量化其在溶液中的浓度具有很大的挑战性。在此，我们开发了一种新方法，通过监测水杨酸（SA）的损失来准确测量过氧化氢（HO）的紫外线光解过程中产生的·OH 的稳态浓度和总·OH 剂量。这种方法仅使用台式紫外可见光谱即可获得信息，从而通过消除对复杂仪器的需求，扩展了资源有限的实验室的测量能力。为了提高与之前方法相比测量 SA 损失速率的精度，我们应用主成分分析（PCA）来拟合在·OH 暴露期间收集的紫外可见光谱。对于我们的实验条件，包含 12 毫升溶液，其中 HO 的浓度最高为 100 mM，SA 的浓度为 0.07 mM，HO 完全光解过程中的稳态·OH 浓度为 1.33×10-5 M±1.14×10-5 M。与之前使用矩阵分析处理光谱的方法相比，这代表着将测量不确定度的置信区间缩小 95%的不确定性降低了十倍以上。此外，与之前的方法相比，测量的·OH 浓度的方差降低了 100 倍。通过使用 PCA，·OH 的检测限和定量限分别为 5.33×10-5 M 和 1.23×10-5 M。通过建立·OH 浓度、HO 浓度和紫外线暴露时间之间的定量关系，我们还展示了如何计算间接光解在天然水生环境中产生的等效·OH 暴露量。最后，我们使用这种方法证明了浓度高达 300 ppm 的悬浮碳质纳米颗粒的存在不会影响·OH 浓度。
