Enhanced procedural blank control for organic geochemical studies of critical sample material
Enhanced procedural blank control for organic geochemical studies of critical sample material
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DOI：
10.1111/gbi.12183
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发表时间：
2016-09
期刊：
影响因子：
3.7
通讯作者：
Arne Leider;T. C. Schumacher;Christian Hallmann
中科院分区：
文献类型：
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作者：
Arne Leider;T. C. Schumacher;Christian Hallmann
沉积岩的有机污染会在碳氢化合物成分的研究中产生假象，这会对解释地球生物记录产生严重的负面影响。假阳性-即非同生烃生物标志物的情况-在前寒武纪研究中很常见，尽管这些研究付出了大量努力，但仍然存在重大挑战。迄今为止，为区分污染和同生物质而标准化“举证责任”的努力未能产生简单或通用的协议，但需求仍然很大，因为贫沥青岩石和富沥青样品都容易受到假阳性信号的积累。为了确定质量控制的最佳方法，我们通过评估不同空白材料在塑料袋中储存期间吸附碳氢化合物的能力来测试其收集环境污染物的能力，并发现常用的石英砂不能提供储存或实验室引起的污染的充分措施。砖坯的优点是即使在锯切过程中也可以平行于岩石样品，其特征在于类似的吸附性能差。受矿物学、有机碳含量和表面积的影响，模型黑色页岩可以吸附比砂坯多20倍的污染物，比不含有机物的模型碳酸盐多200倍的污染物。这一观察结果为污染物的看似系统性地层变化的报告和观察结果提供了解释，但在研究不同岩性的贫沥青岩石样品时，主要应提高对程序空白评估的认识，特别是样品与空白比。此外，塑料袋中的碳氢化合物特征与转移到空白材料中的碳氢化合物特征之间的差异突出了明确检测污染源的困难。人造黑色页岩颗粒可以在生物标志物研究中提供增强的污染控制-特别是对于异常脆弱的样品，如前寒武纪岩石，陨石或外星样品返回材料。
Organic contamination of sedimentary rocks can produce artefacts in studies of hydrocarbon composition, and this can have significant negative consequences for interpretations of the geobiological record. False positives – that is cases of non‐syngenetic hydrocarbon biomarkers – are common in Precambrian studies, and significant challenges persist despite the intensive effort devoted to these studies. Efforts to standardize the ‘burden of proof’ for distinguishing between contamination and syngenetic material have to date failed to yield a simple or universal protocol, yet the need remains great, as both bitumen‐lean rocks and bitumen‐rich samples can be vulnerable to the accumulation of false‐positive signals. In an effort to determine the best approach to quality control, we tested the capability of different blank materials to collect ambient contamination by assessing their capacity to adsorb hydrocarbons during storage in plastic bags and found that commonly used Quartz sand does not provide an adequate measure of storage‐ or laboratory‐induced contamination. Brick blanks, having the advantage that they can parallel rock samples even during the sawing process, are characterized by similar poor adsorption properties. Primarily steered by mineralogy, organic carbon content and surface area, model‐black shales can adsorb up to 20 times more contaminants than sand blanks and up to 200 times more contaminants than organic‐free model‐carbonates. This observation provides an explanation for reports and observations of seemingly systematic stratigraphic variation of contaminants, but mostly should raise awareness for the evaluation of procedural blanks, in particular of sample‐to‐blank ratios, when studying bitumen‐lean rock samples of varying lithologies. Additionally, differences between the hydrocarbon profiles in plastic bags and the hydrocarbon signatures transferred to blank materials emphasize difficulties in the unequivocal detection of contamination sources. Artificial black shale pellets can provide enhanced contamination control in biomarker studies – particularly for exceptionally vulnerable samples such as Precambrian rocks, meteorites or extraterrestrial sample‐return material.