Guo Jingjing, Zong Xiulan, de Winter Niels J, Goudsmit-Harzevoort Barbara, Peterse Francien, Ziegler Martin
Department of Earth Sciences, Faculty of Geoscience, Utrecht University, Utrecht, The Netherlands.
Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, China.
Rapid Commun Mass Spectrom. 2023 Sep 15;37(17):e9597. doi: 10.1002/rcm.9597.
Embedding resins are widely used to fix carbonates for high-precision sample preparation and high-resolution sampling. However, these embedding materials are difficult to remove after sample preparation and are known to affect the accuracy of carbonate stable isotope analyses. Nevertheless, their impact on clumped isotope analysis, which is particularly sensitive to contamination artifacts, has so far not been tested. The observation that running resin-containing samples decreased the reproducibility of clumped isotope values for internal laboratory carbonate standards and increased the external standard deviation (SD 0.061-0.088‰) compared to the long-term observations (0.034‰), prompted us to set up an experiment to test the influence of resin addition on instrument performance.
Here we analyzed the stable and clumped isotope composition of a pure calcium carbonate standard (ETH-4) mixed with three types of embedding resins in 2:1 and 1:1 proportions. Our aim was to assess how resin addition affects isotope analyses.
We found that none of the stable isotopic values were significantly different. The δ C values were -10.22 ± 0.07‰ (mean ± SD) for pure ETH-4, while the δ C values of ETH-4 mixed with embedding resins in 2:1 and 1:1 proportions were -10.21 ± 0.06‰ and -10.18 ± 0.06‰, respectively (p > 0.05). The δ O values were -18.82 ± 0.11‰ for pure ETH-4 versus -18.81 ± 0.09‰ and -18.82 ± 0.08‰ for 2:1 and 1:1 ETH-4:resin mixtures, respectively (p > 0.05). Given the large uncertainty in our results, we did not find significant differences between different mixtures in the carbonate clumped isotope values (Δ ), with 0.458 ± 0.107‰, 0.464 ± 0.086‰, and 0.417 ± 0.089‰ in pure ETH-4 and ETH-4 with 2:1 and 1:1 resin mixtures, respectively (p > 0.05). However, a resin-related bias in the results might be masked by the large uncertainty. The measured ETH-4 values in our study are similar to the InterCarb values (δ C = -10.20‰, δ O = -18.81‰, Δ = 0.450‰, InterCarb-Carbon Dioxide Equilibrium Scale). However, the external SD of Δ in sessions measuring ETH-4 with resins is higher than in sessions without deliberate resin addition for the same measuring period.
We find that the potential contamination from the resin addition leads to a larger variability for Δ values in sessions measuring ETH-4 including resins. We therefore recommend purification of embedded samples using a contamination trap with Porapak prior to analysis, if possible, or avoiding resins during sample preparation and workup, as well as monitoring the measurement quality during and after sessions with samples containing embedding resins.
包埋树脂广泛用于固定碳酸盐，以进行高精度样品制备和高分辨率采样。然而，这些包埋材料在样品制备后难以去除，并且已知会影响碳酸盐稳定同位素分析的准确性。尽管如此，它们对团簇同位素分析的影响（团簇同位素分析对污染假象特别敏感）迄今为止尚未得到测试。观察到运行含树脂样品会降低内部实验室碳酸盐标准品的团簇同位素值的重现性，并且与长期观测值（0.034‰）相比增加了外部标准偏差（SD为0.061 - 0.088‰），这促使我们开展一项实验来测试添加树脂对仪器性能的影响。
在此，我们分析了一种纯碳酸钙标准品（ETH - 4）与三种类型的包埋树脂按2:1和1:1比例混合后的稳定同位素和团簇同位素组成。我们的目的是评估添加树脂如何影响同位素分析。
我们发现所有稳定同位素值均无显著差异。纯ETH - 4的δC值为 - 10.22 ± 0.07‰（平均值±标准差），而与包埋树脂按2:1和1:1比例混合的ETH - 4的δC值分别为 - 10.21 ± 0.06‰和 - 10.18 ± 0.06‰（p > 0.05）。纯ETH - 4的δO值为 - 18.82 ± 0.11‰，而2:1和1:1的ETH - 4:树脂混合物的δO值分别为 - 18.81 ± 0.09‰和 - 18.82 ± 0.08‰（p > 0.05）。鉴于我们结果中的不确定性较大，我们未发现不同混合物在碳酸盐团簇同位素值（Δ）上存在显著差异，纯ETH - 4以及与2:1和1:1树脂混合物的ETH - 4的Δ值分别为0.458 ± 0.107‰、0.464 ± 0.086‰和0.417 ± 0.089‰（p > 0.05）。然而，结果中与树脂相关的偏差可能被较大的不确定性所掩盖。我们研究中测得的ETH - 4值与国际碳酸盐同位素比对组织（InterCarb）的值相似（δC = - 10.20‰，δO = - 18.81‰，Δ = 0.450‰，InterCarb - 二氧化碳平衡标度）。然而，在使用树脂测量ETH - 4的实验中，Δ的外部标准差高于在相同测量周期内未故意添加树脂的实验。
我们发现添加树脂带来的潜在污染导致在测量含树脂的ETH - 4的实验中Δ值的变异性更大。因此，我们建议如果可能的话，在分析前使用装有Porapak的污染捕集器对包埋样品进行纯化，或者在样品制备和后处理过程中避免使用树脂，并在使用含包埋树脂样品的实验期间和之后监测测量质量。
