Optimization of acid digestion conditions on the extraction of fatty acids from stalagmites

Abstract

Lipids in stalagmites have been shown the potential for the paleoclimate reconstruction. However, the low lipid content leads to the difficulty in gaining high resolution lipid record in stalagmites because large mass of samples are required. Previous studies have validated that the acid digestion can improve the yield of lipids, especially fatty acids (FAs) and 3-hydroxy fatty acids (3-OH-FAs). In order to obtain more content of FAs and 3-OH-FAs with limited stalagmite sample weight, we investigate here how the acid digestion conditions (HCl concentration, heating temperature and time duration) could affect the yields of FAs and 3-OH-FAs. Under different concentration of HCl, from 2.0 to 6.0 mol/L, the FAs keep the same step in content variation with 3-OH-FAs, and the highest yields of both two appeared under the 3 mol/L HCl. The content of 3-OH-FAs increases positively with the heating temperature from 80°C to 150°C, while FAs showed the highest content at 130°C. Both of FAs and 3-OH-FAs firstly increased to a high content and then decreased as the heating time duration varies from 1.0 to 4.0 h, with the highest yields of both two being at 3.0 h. Consequently, we suggest the optimized acid digestion condition is under 3 mol/L HCl, heating at 130°C for 3 h and 5 g of each stalagmite sample are sufficient for the lipid analysis.

Keywords

stalagmite / lipids / acid digestion / optimization

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Acknowledgements

This work was supported by the National Basic Research Program of China (No. 2011CB808800), the National Natural Science Foundation of China (Grant Nos. 40930210 and 41130207), and the 111 Project of Education of Ministry of China (No. B08030), and the MOST Special Fund from the State Key Laboratory of Geological Processes and Mineral Resources (MSFGPMR200804, MSFGPMR200904). We thank Dr. Yang Pu and Miss Jun Cao for their help during samples preparation and experiments and two anonymous reviewers for comments on the manuscript.

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