HPLC-QQQ-MS

     We employed an Agilent 1200 series high-performance liquid chromatography- 6460A triple quadrupole-mass spectrometer (HPLC-QQQ-MS) equiped with an autosampler and a masshunter quanlitative workstation in 2009 (Fig.1). The advantage of this LC-MS is its high sensitivity and a wide linear dynamic range for the quantification of organic compounds. The target molecules of this instrument include glycerol dialkyl glycerol tetraethers (GDGTs), bacteriopolyhopanols (BHPs), ladderane fatty acids, intact polar lipids (IPL) and heterocyst glycolipids, which are membrane lipids that are increasingly important and useful in paleoenvironment reconstruction and biogeochemistry study. We now focus on GDGTs and developed a variety of methods to analyze them. Due to a high sensitivity and a low detection limit (~10pg) for the GDGT analysis, this instrument can be used to quantify GDGTs in stalagmites as well as sediments dated back as early as Permian, where only trace amounts of GDGTs were present. This allows to develop and use GDGT proxies in very ancient sedimentary achives to reconstruct temperature and hydroclimate. Over the last decade, we investigated the environmental controls on GDGTs in a wide range of sedimentary achives, including mineral soils, peats, stalagmites, lake sediments, and marine sediments across China and developed new temperature and hydroclimate proxies based on GDGTs, i.e. SSM and Ri/b, with applications in loess-paleosols over the last 350 ka. These work has been published in high-quality journals, e.g. Geology, EPSL and GCA, and has received wide attention.

Fig.1  Agilent 1200 HPLC-6460A QQQ-MS

     We participated in the second round-robin study with 35 laboratories in which GDGTs in pure isolates, lipid extracts and sediments were analyzed. The peformance of our instrument is excellent, showing a high reproducibility and a high precision (Fig. 2). This gurantees the quanlity of GDGT data analyzed from this instrument. Over the last few years, we have provided services of GDGT analysis for a number of collaborators from China and abroad.

Fig. 2 The second round-robin study with 35 laboratories across the globe where GDGTs were analyzed (Schouten et al., 2013). Data from our LC-MS showed excellent reproducibility and precision. Lab code 6 denotes data from our lab.

     Recently, we have developed a new LC methodology to separate the 5- and 6-methyl isomers of brached GDGTs, a suite of GDGT compounds useful in temperature and pH reconstruction in loess-paleosols and lake sediments. This new method has been widely used by laboratories across the globe and leads to identification of novel brGDGT isomers, e.g. 7-methyl brGDGTs and late-eluting isomer of tetramethylated brGDGTs, which are potentially important in paleoenvironmental reconstructions (Fig.3).

Fig. 3  The new LC methodology developed for the separation of 5- and 6-methyl brGDGTs (right panel) results in a better chromatographic separation of isomers than the previous method (left panel)(Yang et al., 2015, OG)