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Separation of Branched and Isoprenoid Glycerol Dialkyl Glycerol Tetraether (GDGT) Isomers in Peat Soils and Marine Sediments Using Reverse Phase Chromatography
Frontiers in Marine Science ( IF 3.7 ) Pub Date : 2020-09-18 , DOI: 10.3389/fmars.2020.539601
Jayne E. Rattray , Rienk H. Smittenberg

Over the last decade, glycerol dialkyl glycerol tetraethers (GDGTs) have become one of the most investigated lipid classes in marine and terrestrial organic geochemical research. GDGTs are microbial membrane core lipids biosynthesized as multiple homolog series of isoprenoid or methyl-branched isomers [isoprenoid glycerol dialkyl glycerol tetraethers (isoGDGTs) and Branched GDGTs (brGDGTs), respectively], whose relative abundance depend on a range of environmental parameters, including temperature. This has led to the development of GDGT-based temperature proxies. A key aspect in the analysis of GDGTs and the further development of their use as environmental proxies is good chromatographic separation of the full range of structural and stereo-isomers, with potential for discovery of novel GDGT variants. Several HPLC methods have been developed to this extent, but partial co-elution of GDGTs remains an issue despite long run times. In this study, we investigate the effects of different types of reverse phase (RP) chromatography on the separation of GDGT isomers. We found that the use of a Kinetex C18-XB column gives good separation of isoGDGT isomers in comparison to the recently developed double column HILIC analysis operated in normal phase (NP) and has a shorter run time. In marine samples, the regularly reported isoprenoid GDGTs separated in a similar way as in NP, however an earlier eluting group was observed to elute with the crenarchaeol isomer used in the TEX86 proxy. In a Swedish peat bog sample, a large range of isoGDGT isomers were observed. We observed a range of brGDGT isomers in several samples often with near baseline separation. Exact identification of all these isomers remained elusive, due to the different mechanism of separation in RP, and the complexity of the brGDGT family. The C18-XB method is rapid and versatile and can be set up on either low-pressure HPLC systems (max 400 bar) with a sample run time of 25 min for brGDGTs and 45 min to include isoGDGTs. On UHPLC-MS systems (>600 bar) the sample run time is reduced to 15 min. Most importantly, the C18-XB method presented here gives unusual separation of both isoprenoid and brGDGTs and could be a useful tool for the further elucidation of the biological sources and environmental factors that play a role in the production of different GDGT isomers.

中文翻译:

使用反相色谱分离泥炭土壤和海洋沉积物中支链和类异戊二烯甘油二烷基甘油四醚 (GDGT) 异构体

在过去十年中,甘油二烷基甘油四醚 (GDGT) 已成为海洋和陆地有机地球化学研究中研究最多的脂质类别之一。GDGT 是生物合成的微生物膜核心脂质,作为类异戊二烯或甲基支链异构体的多个同源系列 [异戊二烯甘油二烷基甘油四醚 (isoGDGTs) 和支链 GDGTs (brGDGTs),分别],其相对丰度取决于一系列环境参数,包括温度. 这导致了基于 GDGT 的温度代理的开发。GDGT 分析及其作为环境指标的进一步发展的一个关键方面是对所有结构和立体异构体进行良好的色谱分离,具有发现新 GDGT 变体的潜力。在这种程度上已经开发了几种 HPLC 方法,但尽管运行时间长,GDGT 的部分共洗脱仍然是一个问题。在本研究中,我们研究了不同类型的反相 (RP) 色谱对 GDGT 异构体分离的影响。我们发现,与最近开发的在正相 (NP) 中操作的双柱 HILIC 分析相比,使用 Kinetex C18-XB 色谱柱可以更好地分离 isoGDGT 异构体,并且运行时间更短。在海洋样品中,定期报告的类异戊二烯 GDGT 以与 NP 中类似的方式分离,但观察到较早的洗脱组与 TEX86 代理中使用的 crenarchaeol 异构体一起洗脱。在瑞典泥炭沼泽样品中,观察到了大范围的 isoGDGT 异构体。我们在几个样品中观察到一系列 brGDGT 异构体,通常具有接近基线的分离。由于 RP 中不同的分离机制以及 brGDGT 家族的复杂性,所有这些异构体的准确鉴定仍然难以捉摸。C18-XB 方法快速且通用,可以在低压 HPLC 系统(最大 400 bar)上设置,brGDGT 的样品运行时间为 25 分钟,isoGDGT 的样品运行时间为 45 分钟。在 UHPLC-MS 系统 (>600 bar) 上,样品运行时间减少到 15 分钟。最重要的是,这里介绍的 C18-XB 方法对类异戊二烯和 brGDGT 进行了不寻常的分离,并且可以成为进一步阐明在不同 GDGT 异构体生产中发挥作用的生物来源和环境因素的有用工具。C18-XB 方法快速且通用,可以在低压 HPLC 系统(最大 400 bar)上设置,brGDGT 的样品运行时间为 25 分钟,isoGDGT 的样品运行时间为 45 分钟。在 UHPLC-MS 系统 (>600 bar) 上,样品运行时间减少到 15 分钟。最重要的是,这里介绍的 C18-XB 方法对类异戊二烯和 brGDGT 进行了不寻常的分离,并且可以成为进一步阐明在不同 GDGT 异构体生产中发挥作用的生物来源和环境因素的有用工具。C18-XB 方法快速且通用,可以在低压 HPLC 系统(最大 400 bar)上设置,brGDGT 的样品运行时间为 25 分钟,isoGDGT 的样品运行时间为 45 分钟。在 UHPLC-MS 系统 (>600 bar) 上,样品运行时间减少到 15 分钟。最重要的是,这里介绍的 C18-XB 方法对类异戊二烯和 brGDGT 进行了不寻常的分离,并且可以成为进一步阐明在不同 GDGT 异构体生产中发挥作用的生物来源和环境因素的有用工具。
更新日期:2020-09-18
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