Study on Influence Factors for Determination of Oxygen Isotopic Composition of Silicates and Oxide Minerals by BrF5 Method
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摘要: 应用五氟化溴法（BrF5）测定硅酸盐及氧化物矿物的氧同位素组成，试剂纯化、样品预处理、环境湿度、反应器洁净程度以及实验质量控制是影响该法准确度的主要因素。为确定BrF5法最佳实验条件，提高分析精度，本文以国家标准物质为参考，对硅酸盐及氧化物矿物在不同焙烧温度下的氧同位素组成进行分析，并对实验环境湿度和反应器洁净程度对分析数据质量的影响进行了系统研究。实验确定了焙烧温度设置为650~750℃，可去除硅酸盐全岩样品中的炭质成分，避免了温度因素引起的同位素分馏；将实验环境相对湿度降低至50% RH，并在0.5min内完成样品装填，可解决由于水汽造成δ18O值明显偏低的突出问题；对于新使用的反应器，或反应器在使用中有黄色物质脱落、内壁受到污染，及时进行氟化处理和清洗，可避免因氧气产率降低所引起的氧同位素分馏；反应器交替进行样品和标准物质CO2试样的制备，可对样品同位素数据的可靠性进行监测。对国家标准GBW04409的氧同位素组成进行测试，δ18O测试结果与推荐值一致，分析精度优于0.1‰。以上途径有效控制了氧同位素分馏，提高了BrF5氧同位素分析方法的适用性。Abstract:
BACKGROUNDReagent purification, sample pretreatment, environmental humidity, reactor cleanliness and experimental quality control are the main influence factors for determination of oxygen isotopic composition of silicates and oxide minerals by BrF5 method. OBJECTIVESTo determine the optimal experimental conditions and improve the accuracy by selecting silicates and oxide minerals as laboratory raw materials for oxygen isotopic composition analysis. To discuss the influence factors for determination of oxygen isotopic composition of silicates and oxide minerals by BrF5 method. METHODSUsing BrF5 analysis method and taking standard sample as the reference, oxygen isotopic compositions of silicates and oxide minerals were determined at different calcination temperatures. At the same time, the effects of environmental humidity and reactor cleanliness on the analytical results were also studied. RESULTSThe results show that 650-750℃ is the best calcination temperature range for removing carbon components during oxygen isotope analysis, which can avoid the isotope fractionation caused by temperature. By reducing the relative environment humidity or the sample loading time within 0.5min, the lower δ18O values caused by vapor was improved. The new reactor, or the reactor with large yellow substance falling off, or the contaminated reactor will reduce the yield of oxygen and cause oxygen isotope fractionation, so the reactors should be fluorinated or purged in time. The sample and standard material is loaded alternately for each reactor to monitor the reliability of the isotopic composition of the sample. The results of oxygen isotopic composition of GBW04409 are consistent with the recommended values. The relative standard deviation is better than 0.1‰ for δ18O under the optimized conditions. CONCLUSIONSThe proposed method can effectively control oxygen isotope fractionation and improve the applicability of BrF5 oxygen isotope analysis method. -
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表 1 在不同焙烧温度下测定样品的有机碳含量及颜色变化情况
Table 1. Measured organic carbon content in samples and their color information at different calcination temperature
焙烧温度
(℃)黑色含炭质硅质页岩
(Sa-1)黑色含炭质黏土质页岩
(Sa-2)有机碳含量
(%)样品颜色 有机碳含量
(%)样品颜色 100 4.3825 黑色 2.1145 黑色 150 4.3765 黑色 2.1142 黑色 200 4.3124 黑色 2.0116 黑色 250 4.2939 黑色 1.9427 浅黑色 300 4.2276 浅黑色 1.8739 浅黑色 350 3.0262 浅黑色 1.4662 浅灰色 400 1.5870 浅灰黑色 0.2394 浅灰色 450 0.6530 浅灰色 0.1695 灰白色 500 0.0314 浅灰色 0.0374 灰白色 550 0.0284 灰白色 0.0251 灰白色 600 0.0211 灰白色 0.0088 灰白色 650 0.0090 灰白色 0.0076 灰白色 700 0.0024 灰白色 0.0053 灰白色 750 0.0021 灰白色 0.0035 灰白色 800 0.0016 灰白色 0.0015 灰白色 850 0.0011 灰白色 0.0012 灰白色 900 0.0008 灰白色 0.0009 灰白色 950 0.0008 灰白色 0.0008 灰白色 1000 0.0006 灰白色 0.0008 灰白色 
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