索氏提取-原子荧光光谱法测定含油岩心中的汞和砷

Determination of Mercury and Arsenic in Oil-bearing Core by Soxhelt Extraction-Atomic Fluorescence Spectrometry

原油对测定含油岩心中的汞和砷有很大影响,目前去除原油等有机物的方法主要有高温烧制、强酸高温氧化等,要求反应温度较高,会造成汞和砷的损失而使测定结果偏低。本文采用索氏提取法,以氯仿作为提取剂在75℃下低温提取分离岩心中的原油,再用50%的王水溶解剩余样品,原子荧光光谱法测定汞和砷的含量。该方法对汞和砷的检出限分别为0. 003mg/kg和0. 10mg/kg,相对标准偏差分别为7. 3%和5. 1%,加标回收率均大于92. 5%。与传统方法相比较,该方法避免了由于原油的疏水性造成样品与王水接触不充分、样品分解不完全和反应温度过高导致汞元素损失的问题,测定汞的相对标准偏差由33. 0%降低至7. 3%,测定砷的相对标准偏差由25. 0%提高至5. 1%,为含油岩心中其他元素的检测提供了借鉴。

BACKGROUND: Crude oil had a great influence on the determination of mercury and arsenic in oil-bearing cores by atomic fluorescence spectrometry. At present,the main methods of removing organic matter such as crude oil are high-temperature firing and high-temperature oxidation with strong acid. In these methods,high reaction temperature will cause loss of mercury and arsenic,resulting in lower results.OBJECTIVES: To develop a separation method with low operating temperature.METHODS: Mercury and arsenic in oil-bearing cores were determined by atomic fluorescence spectrometry with Soxhlet extraction at a low temperature for this method of 75℃ and the remaining part was decomposed by 50%aqua regia.RESULTS: The detection limits were 0. 003 mg/kg and 0. 10 mg/kg for mercury and arsenic,respectively. The relative standard deviations were 7. 3% and 5. 1%,respectively. The relative standard deviation of mercury decreased from 33. 0% to 7. 3%,and the relative standard deviation of arsenic decreased from 25. 0% to 5. 1%.The recoveries of standard addition were greater than 92. 5%.CONCLUSIONS: Compared with traditional methods,this method avoided the problems of insufficient contact between samples and aqua regia due to the hydrophobicity of crude oil,incomplete decomposition of samples and mercury loss due to excessive reaction temperature. The proposed method provides a reference for the determination of other elements in oil-bearing cores.