Grass Material as a Modern Process Standard for 14C Analysis of n-Alkanes
Grass Material as a Modern Process Standard for 14C Analysis of n-Alkanes
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草材料作为正烷烃 14C 分析的现代工艺标准
DOI：
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发表时间：
2016
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通讯作者：
J. Dungait
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作者：
L. Cisneros;X. Xu;C. Bryant;E. Pearson;J. Dungait
摘要报告化合物特定放射性碳分析(CSRA)准确的放射性碳结果的困难之一是缺乏合适的过程标准物质来校正在广泛的样品处理过程中添加的碳的数量和14C含量。我们评价了从现代牧草原料中提取的正构烷烃(现代分数为1.224±0.006)作为CSRA工艺标准的使用情况。用制备毛细管气相色谱(PCGC)从两种独立的化学提取方法中分离出正构烷烃。由于这是我们第一次评估草类正构烷烃的14C含量，我们使用商业上可获得的现代含量和14C含量的单一化合物校正了PCGC分离得到的外来碳。两种提取方法的结果是一致的，C29正构烷烃具有一定的现代值，在草体积值的1σ以内，而C31正构烷烃和丰度较低的正构烷烃的值在草体积值的2σ以内。C29和C31正构烷烃是牧草中含量最丰富的正构烷烃，因此更适合收集足够数量的碳用于加速器质谱仪(AMS)分析。我们的结果表明，选择洗脱时间与未知数最接近的草正构烷烃可能是可取的，因为在较晚的洗脱时间可能会受到GC柱出血(14C)的更大影响。我们的结论是，现代牧草中已知14C含量的C29和C31正构烷烃可作为室内标准，以校正正构烷烃14C分析样品制备过程中14C-游离碳的添加。
Abstract One of the difficulties in reporting accurate radiocarbon results from compound-specific radiocarbon analysis (CSRA) is the lack of suitable process standard materials to correct for the amount and 14C content of carbon added during extensive sample processing. We evaluated the use of n-alkanes extracted from modern grass material (1.224±0.006 fraction modern) as process standards for CSRA. The n-alkanes were isolated using preparative capillary gas chromatography (PCGC) from two independent chemical extraction methods applied to the grass. Since this was our first assessment of the 14C content of the grass n-alkanes, we corrected for extraneous carbon derived from PCGC isolation using commercially available single compounds of modern and 14C-free content. Results were consistent across the two extraction methods showing that the C29 n-alkane has a fraction modern value that is within 1σ of the bulk value of the grass while C31 n-alkane and less abundant n-alkanes have values within 2σ of the bulk value of the grass. C29 and C31 n-alkanes were the most abundant n-alkanes in the grass and, as such, the more feasible for collection of sufficient amounts of carbon for accelerator mass spectrometry (AMS) analysis. Our results suggest that choosing a grass n-alkane with an elution time closest to that of the unknowns may be advisable due to possibly greater effect from GC column bleed (14C-free) at later elution times. We conclude that C29 and C31 n-alkanes in modern grass of known 14C content can be used as in-house standards to correct for the addition of 14C-free carbon during sample preparation for 14C analysis of n-alkanes.