Abstract Archaeal isoprenoidal glycerol dibiphytanyl glycerol tetraether lipids (iGDGTs) and their non-isoprenoidal branched bacterial analogues (brGDGTs) have widespread applications in biogeochemistry and paleothermometry. Analysis of GDGTs usually involves separation using high performance liquid chromatography, typically coupled via atmospheric pressure chemical ionisation to mass spectrometric detection in selected ion-monitoring mode (HPLC–APCI-MS). However, reliable determination of ratios and, in particular, quantification by this technique, can be challenging due to differences in ionisation efficiencies of the various compounds. Quantification of GDGTs also relies on external calibration of the relative response to an internal standard with authenticated GDGTs, which are often not readily accessible. Here, we tested the suitability of high temperature gas chromatography with flame ionisation detection (HTGC-FID) for the determination of concentrations and tetraether lipid-based ratios in marine and terrestrial samples. For this, we identified GDGTs in environmental samples using HTGC coupled to time-of-flight mass spectrometry (HTGC–MS). Using a purified GDGT standard, we show we can quantify GDGT-0 in environmental samples by GC-FID. Some GDGT-based ratios measured by HTGC-FID exhibited a linear correlation (1:1) with ratios derived from HPLC–MS and weight-based ratios of mixtures of purified standards. However, ratios relying on minor isomers, such as TEX86 and MBT/CBT have many unresolved challenges for determination by HTGC. Detection limits were higher than for HPLC–MS. However, the advantages of employing HTGC-based methods include: (1) the independence from MS tuning-related differences in ionisation energies; (2) the potential for direct comparison with other, non-GDGT based biomarkers; and (3) a more complete insight into biomarker distributions in environmental samples by the extension of the temperature range. Quantitative elution of GDGTs from a HTGC column as demonstrated herein, will also enable their analysis by compound-specific isotope ratio mass spectrometry.

中文翻译：

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环境样品中古菌和细菌甘油二烷基甘油四醚 (GDGT) 脂质的高温气相色谱与火焰电离和飞行时间质谱检测

摘要 古菌类异戊二烯甘油二联植烷甘油四醚脂质 (iGDGTs) 及其非类异戊二烯分支细菌类似物 (brGDGTs) 在生物地球化学和古温度测量中具有广泛的应用。GDGT 的分析通常涉及使用高效液相色谱进行分离，通常通过大气压化学电离与选定离子监测模式 (HPLC-APCI-MS) 中的质谱检测相结合。然而，由于各种化合物的电离效率不同，因此可靠地确定比率，尤其是通过这种技术进行量化可能具有挑战性。GDGT 的量化还依赖于对具有经认证的 GDGT 的内部标准的相对响应的外部校准，这通常不容易获得。这里，我们测试了使用火焰电离检测器 (HTGC-FID) 的高温气相色谱法测定海洋和陆地样品中的浓度和基于四醚脂质的比率的适用性。为此，我们使用与飞行时间质谱联用 (HTGC-MS) 的 HTGC 鉴定了环境样品中的 GDGT。使用纯化的 GDGT 标准，我们表明我们可以通过 GC-FID 量化环境样品中的 GDGT-0。通过 HTGC-FID 测量的一些基于 GDGT 的比率与来自 HPLC-MS 的比率和纯化标准混合物的基于重量的比率呈现线性相关性 (1:1)。然而，依赖于次要异构体的比率，如 TEX86 和 MBT/CBT，在 HTGC 测定方面存在许多未解决的挑战。检测限高于 HPLC-MS。然而，采用基于 HTGC 的方法的优点包括：(1) 独立于 MS 调谐相关的电离能差异；(2) 与其他非基于 GDGT 的生物标志物直接比较的潜力；(3) 通过扩展温度范围，更全面地了解环境样品中的生物标志物分布。如本文所示，从 HTGC 柱中定量洗脱 GDGT 也将能够通过化合物特定的同位素比质谱法对其进行分析。