紫外可见分光光度法间接测定钒储能介质中亚硫酸根的含量

UV-Vis Spectrophotometric Indirect Determination of Sulfite in Vanadium Energy-Storage Medium

自行设计并组装了SO2的蒸馏装置。定量移取钒储能介质样品置于250mL的蒸馏瓶中,加水至溶液体积约为125mL。在200mL·min^-1的流量向瓶中通入氩气的条件下,于140℃油浴中恒温加热蒸馏20min。在通氩气及样品注入之前,先在吸收管中预置2.00g·L^-1无水乙酸铅溶液10mL,在蒸馏过程中蒸出的SO2与Pb^2+反应定量生成PbSO3沉淀。蒸馏结束时,向吸收管中加入碘饱和溶液20mL,反应3min后将吸收液完全转移至100mL棕色容量瓶中,加入盐酸200μL,加水稀释至100.0mL,在加入碘溶液并反应3min期间,PbSO3沉淀被I2氧化成PbSO4沉淀并同时定量产生I3^-。在波长287nm处测定溶液中I3^-的吸光度,据此间接测得SO2的质量浓度。在溶液中加入盐酸的作用是消除沉淀的干扰,并使溶液的吸光度稳定。工作曲线系取亚硫酸钠标准溶液按上述方法先后加入乙酸铅溶液及碘溶液,但无需经过蒸馏过程。测得SO2的质量浓度在3.0mg·L^-1以内与其相应吸光度呈线性关系。按此方法分析了2件样品(A和B),测得样品中SO2的含量分别为1.60,0.49mg·L^-1,测定值的相对标准偏差(n=10)分别为2.5%,4.2%。以其中一个样品为基体,在3个浓度水平(0.85,1.69,2.54mg·L^-1)上进行回收试验,测得回收率依次为89.4%,93.5%,102%。

A self-designed SO2-distillation apparatus was fabricated. A definite volume of the vanadium energy-storage medium was transferred quantitatively into the 250 mL distillation flask of the apparatus and water was added to make its volume to ca. 125 mL. Under the condition of passing Ar-gas through the solution at a flow rate of 200mL·min^-1 , the distillation of SO2 was performed by heating the distillation flask in a oil-bath at a constant temperature of 140℃ for 20 min. Before the passing of Ar-gas and introduction of sample solution, 10 mL of 2.00g·L^-1 anhydrous lead acetate solution were added into the absorption tube of the apparatus preliminarily. During the course of distillation, SO2 in the distillate reacts with Pb^2+ to form PbSO3 precipitate in the absorption tube. At the end of distillation, 20 mL of sat d solution of iodine were added to the tube to react with PbSO3 for 3 min, giving PbSO4 and I3^- quantitatively due to oxidation by iodine. After reaction for 3 min the solution was transferred into a brown-glass 100 mL volumetric flask and after adding 200 μL cone. HCl, the solution was diluted to 100.0 mL with water, mixed thoroughly, and absorbance of the solution at 287 nm due to the presence of I3^- was measured, and mass concentration of SO2 was obtained indirectly on the base of the absorbance value obtained. The action of cone. HC1 added to the solution was to eliminate interference of precipitate and to make the absorbance of the solution stable. Working curve was prepared with a set of solutions containing standard Na2 SO3 solution in various concentrations and treated in the same procedure by adding Pb (Ac)2 solution and sat'd I2 solution in succession and etc, but without distillation. It was found that linearity range for SO2 was found with in 3.0 mg·L^-1. Two substantial samples (A and B) were analyzed by this method giving SO2 contents of 1.60 mg·L^-1 and 0.49 mg·L^-1 and values of RSDs (n = 10) 2.5% and 4.2% respectively. Recovery was tested by using sample A as matrix and addition of standard solution at 3 concentration levels (0.85,1.69 and 2.54 mg·L^-1 ) giving results of recovery 89.4 %, 93.5% and 102% respectively.