Comprehensive analysis of laboratory boron contamination for boron isotope analyses of small carbonate samples
Comprehensive analysis of laboratory boron contamination for boron isotope analyses of small carbonate samples
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DOI：
10.1016/j.chemgeo.2021.120280
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发表时间：
2021-04
期刊：
影响因子：
3.9
通讯作者：
K. Kubota;T. Ishikawa;K. Nagaishi;T. Kawai;T. Sagawa;M. Ikehara;Y. Yokoyama;T. Yamazaki
中科院分区：
文献类型：
--
作者：
K. Kubota;T. Ishikawa;K. Nagaishi;T. Kawai;T. Sagawa;M. Ikehara;Y. Yokoyama;T. Yamazaki
在古气候学研究中，硼同位素作为海洋碳酸盐的代用指标被广泛应用于海水pH和大气pCO 2的重建，而这需要精确的硼同位素分析。硼同位素组成的测定容易受到污染，特别是对于含有少量硼的样品分析;然而，实验和实验室污染的来源没有明确评估。在这项研究中，硼和硼同位素污染的小碳酸盐样品的分析过程中进行了详细检查，在样品清洗，样品储存，化学分离，和同位素测量。使用H2O和超声波反复清洗有孔虫壳可有效减少富含粘土材料的硼污染;但是，建议使用甲醇和H2 O2进行额外的清洗步骤，以获得可重复的精确δ 11 B、δ 18 O和Mg/Ca值。样品在玻璃小瓶中储存期间的硼污染远大于预期。附着在有孔虫壳体上的玻璃源硼不能被任何物理或化学清洗过程完全去除，并显著影响δ11B值。即使在实验室中使用低硼HEPA、无硼HEPA或ULPA过滤器进行空气处理，气态硼的空气污染仍然很严重，丰度和同位素组成存在季节性变化。虽然这会影响化学分离过程中硼的程序空白，但除酸化学过滤器可以减少空气中的硼通量。MC-ICPMS分析中的自动进样器可能是空气中硼污染的另一个来源。
Boron isotopes are widely used as a proxy of marine carbonate in paleoclimatology to reconstruct seawater pH and atmosphericpCO2, and precise and accurate boron isotopic analysis is required for this purpose. Determination of boron isotopic composition is susceptible to contamination, especially for sample analyses with small amounts of boron; however, sources of experimental and laboratory contamination are not clearly evaluated. In this study, boron and boron isotope contamination during the analysis of small carbonate samples were examined in detail during sample cleaning, sample storage, chemical separation, and isotope measurement. Repeated cleaning of foraminifera shells using H2O with ultrasonication effectively minimized boron contamination from clay-rich material; however, an additional cleaning step with methanol and H2O2is recommended to obtain repeatable precise δ11B, δ18O, and Mg/Ca values. Boron contamination during sample storage in a glass vial was far greater than expected. Glass-derived boron attached to foraminifera shells could not be completely removed by any physical or chemical cleaning process and influenced the δ11B value significantly. Even when a low-boron HEPA, boron-free HEPA, or ULPA filter was used for air-handling in the laboratory, airborne contamination by gaseous boron can still be significant, with seasonal variation in abundance and isotopic composition. Although this affects the procedural blank of boron during chemical separation, an acid-removing chemical filter can reduce the airborne boron flux. An autosampler in the MC-ICPMS analysis might be an additional source of airborne boron contamination.