燃烧碘量光电滴定法测定含氯地质样品中硫

Determination of sulfur in chlorine-containing geological sample by combustion iodimetry photoelectric titration

燃烧碘量法是分析硫的经典方法,但将其应用于地质样品分析时,样品中的氯会对测定产生干扰。实验在对助熔剂、样品燃烧分解温度和滴定方式优化的基础上,以数学方程校正法消除了氯对硫的干扰,建立了燃烧碘量光电滴定法测定地质样品中硫的方法。实验表明,控制温度为1 250~1 300℃时样品可充分燃烧分解;采用低空白值的二氧化硅做为燃烧助熔剂有效降低了方法的检出限;利用以硒光电池电位变化指示终点的方法即光电滴定法替代传统的目视滴定法可弥补因视觉观察而产生的误差,提高了测定结果的准确性。在不同性质(水系沉积物、岩石和土壤)国家标准物质中加入优级纯氯化钠进行氯的干扰试验,结果表明,氯对硫的干扰量与氯的含量呈线性关系,据此,得到了对氯干扰进行校正的数学方程。方法检出限为17.4μg/g、测定下限为58.0μg/g。采用实验方法测定不同性质的地质国家标准物质(土壤和水系沉积物)中硫,结果与认定值的相对误差(RE)为-3.41%^+5.00%,对数差(ΔlgC)为-0.015%^+0.022%,相对标准偏差(RSD,n=12)为0.75%~2.5%。

Combustion iodometry was a classic method for analysis of sulfur.However,when it was applied for analysis of geological sample,chlorine in the sample would cause interference with the determination.Based on the optimization of flux,sample combustion decomposition temperature and titration method,the interference of chlorine with the determination of sulfur was eliminated by mathematical equation correction.Thus,a determination method of sulfur in geological sample was established by combustion iodometry photoelectric titration.The experimental results showed that the sample could be fully combusted and decomposed when the temperature was controlled in range of 1 250-1 300℃.The detection limit of method was effectively reduced by using silicon dioxide with low blank value as combustion flux.The method using the change of selenium cell potential to indicate the reaction endpoint（i.e.,photoelectric titration）was adopted to replace the traditional visual titration,which could make up the error caused by visual observation,thus improving the accuracy of determination results.The sodium chloride of guarantee reagent was added into the national certified reference materials with different properties（stream sediment,rock and soil）for the interference tests of chlorine.The results indicated that the interference amount of chlorine with determination of sulfur was linear to the chlorine content.Accordingly,the mathematical equation for correction of chlorine interference was obtained.The detection limit of method was 17.4μg/g and the low limit of determination was 58.0μg/g.The content of sulfur in national certified reference materials of geological samples with different properties（soil and stream sediment）was determined according to the experimental method.The relative errors（RE）between the results and the certified values were-3.41%-＋5.00%.The logarithmic differences（ΔlgC）were-0.015%-＋0.022%.The relative standard deviations（RSD,n=12）were 0.75%-2.5%.