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

该项目将开发灵敏和节省时间的分析方法，以量化海洋和湖泊环境中一类重要的有机化合物--长链烷酮。烯酮只由属于等鞭藻目的微藻产生，目前还没有其他已知的生物产生这种化合物。这种独特的化合物被称为生物标记物。烯酮生物标记物对分解具有极强的抵抗力，已在1.2亿年前的地质沉积物中发现。值得注意的是，从海洋和湖泊环境中测量的烯酮在不同的生长温度下显示出一致的结构变化，并跟踪水生光合作用生产力。因此，对古代沉积物中的烯烃的测量提供了对过去气候和水生生产力的定量了解。在人类活动导致全球变暖的时代，这些信息有助于预测未来气候和水生生态系统的变化。该项目更广泛的影响包括对一名博士研究生、本科生研究人员和一名高中暑期实习生的支持。传统上，烯烃的分析使用与火焰离子化检测器(GCFID)耦合的气相色谱仪，或者在极低浓度的样品中，使用气相色谱-化学电离质谱仪(GCCIMS)。然而，GCFID是非选择性的(即，如果存在干扰，不能排除干扰)，灵敏度相对较低，需要对复杂样品进行繁琐的样品清理，而GCCIMS对烯烃表现出非线性且往往可变的响应，这增加了分析的不确定性。这项研究利用了高压液相色谱质谱(HPLCMS)的最新进展。初步数据表明，新的基于反相高效液相色谱-质谱仪的分析方法将具有更高的灵敏度(高达两个数量级)和特殊的选择性(即，强大的排除干扰的能力)。建议的工作包括测试各种液相色谱条件(溶剂洗脱方案、柱类型)，以优化长链烯烃的色谱分离。包括两种不同电离模式(常压化学电离或电喷雾电离)的质谱学参数以及各种电子设置也将得到优化。一系列藻类培养样品将在不同的温度下培养，并使用传统的GCFID方法进行测量。然后，这些培养样品将被用作标准，用于校准真实的烯酮代用值和基于HPLCMS的测量。将对从不同海洋环境中收集的大量包含可变干扰的全球海洋表层沉积物进行分析，以全面验证新的反相HPLCMS方法。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.