Comprehensive analysis of alkenones and alkenoates by reversed phase HPLC-MS with unprecedented sensitivity and selectivity

Brown University, Providence RI

Investigators

Abstract

This project will develop sensitive and time-saving analytical methods to quantify an important class of organic compounds, long chain alkenones, in ocean and lake environments. Alkenones are produced only by microalgae belonging to the order Isochrysidales, with no other organisms known to make such compounds. Such unique compounds are termed biomarkers. Alkenone biomarkers are extremely resistant to break-down and have been found in geological sediments as old as 120 million years. Remarkably, alkenones measured from ocean and lake environments display consistent structural changes at different growth temperatures and also track aquatic photosynthetic productivity. Thus, measurement of alkenones in ancient sediments provides quantitative insights to past climate and aquatic productivity. That information helps predict future changes in climate and aquatic ecosystems in the era of global warming induced by human activities. The project Broader Impacts include support for a Ph.D. graduate student, undergraduate student researchers, and a high school summer intern. Traditionally, alkenones are analyzed using gas chromatograph coupled to a flame ionization detector (GCFID), or in extremely low concentration samples, gas chromatograph-chemical ionization mass spectrometry (GCCIMS). However, GCFID is non-selective (i.e., cannot exclude interferences if present) and has relatively low sensitivity and requires tedious sample cleanup for complex samples, whereas GCCIMS displays non-linear and often variable responses to alkenones, which increases analytical uncertainties. The proposed research takes advantage of the latest advances in high pressure liquid chromatograph mass spectrometry (HPLCMS). Preliminary data shows that the new reversed phase HPLC-MS based analytical methods will have much higher sensitivity (up to two orders of magnitudes), and exceptional selectivity (i.e., strong capability to exclude interferences) for analyzing alkenones. The proposed work includes testing various liquid chromatographic conditions (solvent elution schemes, column types) to optimize the chromatographic separation of long chain alkenones. Mass spectrometry parameters including two different ionization modes (atmospheric pressure chemical ionization, or electrospray ionization), and various electronic settings will also be optimized. A series of algal culture samples will be grown at different temperatures and measured using the traditional GCFID method. These culture samples will then be used as standards for calibration between the authentic alkenone proxy values and HPLCMS based measurements. A large set of global ocean surface sediments collected from diverse ocean environments and containing variable interferences will be analyzed to fully validate the new reversed phase HPLCMS methods. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.