IP25 in marine sediments, supplementary material@en

We describe the results of an inter-laboratory investigation into the identification and quantification of the Arctic sea ice biomarker proxy IP25 in marine sediments. 7 laboratories took part in the study, which consisted of the analysis of IP25 in a series of sediment samples from different regions of the Arctic, sub-Arctic and Antarctic, additional sediment extracts and purified standards. The results obtained allowed 4 key outcomes to be determined. First, IP25 was identified by all laboratories in sediments from the Canadian Arctic with inter-laboratory variation in IP25 concentration being substantially larger than within individual laboratories. This greater variation between laboratories was attributed to the difficulty in accurately determining instrumental response factors for IP25, despite provision of appropriate standards. Second, the identification of IP25 by 3 laboratories in sediment from SW Iceland that was believed to represent a blank, was interpreted as representing a better limit of detection or quantification for such laboratories, contamination or mis-identification. These alternatives could not be distinguished conclusively with the data available, although it is noted that the precision of these data was significantly poorer compared with the other IP25 concentration measurements. Third, 3 laboratories reported the occurrence of IP25 in a sediment sample from the Antarctic Peninsula even though this biomarker is believed to be absent from the Southern Ocean. This anomaly is attributed to a combined chromatographic and mass spectrometric interference that results from the presence of a di-unsaturated highly branched isoprenoid (HBI) pseudo-homologue of IP25 that occurs in Antarctic sediments. Finally, data are presented that suggest that extraction of IP25 is consistent between Automated Solvent Extraction (ASE) and sonication methods and that IP25 concentrations based on 7-hexylnonadecane as an internal standard are comparable using these methods. Recoveries of some more unsaturated HBIs and the internal standard 9-octylheptadecene, however, were lower with the ASE procedure, possibly due to partial degradation of these more reactive chemicals as a result of higher temperatures employed with this method. For future measurements, we recommend the use of reference sediment material with known concentration(s) of IP25 for determining and routinely monitoring instrumental response factors. […]本研究报道了一项跨实验室调查的结果，该调查针对海洋沉积物中北极海冰生物标志物替代指标IP25的识别与定量分析展开。本次研究共有7家实验室参与，实验内容包括对北极、亚北极及南极不同区域的一系列沉积物样品、额外沉积物提取物以及纯化标准品中的IP25进行分析。本次研究所得结果可归纳为四项核心结论。其一，所有实验室均在加拿大北极地区的沉积物样品中检出IP25，且实验室间IP25浓度的差异显著大于单个实验室内部的差异。尽管已提供合适的标准品，但实验室间的这种较大差异主要归因于难以精准测定IP25的仪器响应因子。其二，3家实验室在原本被视为空白对照的冰岛西南部沉积物样品中检出了IP25，对此可作出三种解读：一是这些实验室具备更优的检出限或定量限，二是实验存在污染，三是出现了识别偏差。但基于现有数据无法明确区分这三种可能性，且需指出的是，相较于其他IP25浓度测定数据，这批数据的精密度显著更差。其三，有3家实验室在南极半岛的沉积物样品中检测到了IP25，尽管学界普遍认为南大洋中不存在该生物标志物。这一异常现象可归因于色谱与质谱的联合干扰：南极沉积物中存在IP25的二不饱和高支链类异戊二烯（HBI）伪同系物，由此引发了上述干扰。其四，本研究呈现的数据显示，自动溶剂萃取（ASE）与超声萃取两种方法对IP25的萃取效果并无显著差异，且以7-己基十九烷作为内标时，两种方法得到的IP25浓度结果具备可比性。不过，采用ASE方法时，部分更高不饱和度的HBI以及内标9-辛基十七烯的回收率更低，这可能是因为该方法使用的温度更高，导致这些反应性较强的化合物发生了部分降解。针对未来的测定工作，我们建议使用已知IP25浓度的沉积物标准物质，来测定并日常监控仪器响应因子。[…]