 |
CONTACT INFORMATION
EDUCATION Ph.D. candidate , Analytical Chemistry, University of Minnesota Thesis: Fundamental and Applied Studies of Chromatographic Resolving Power for Use in Proteomic Analysis B.S. , Chemistry, Peking University, 2001
RESEARCH SUMMARY 1. Peak Capacity Optimization in Reversed-Phase Gradient Elution Chromatography The last decade has witnessed a huge increase in interest in the analysis of complex biological mixtures, such as those encountered in proteomic research. Currently, reversed-phase liquid chromatography (RPLC) under gradient elution is one of the premier bio-separation techniques due to its high resolving power. Peak capacity, the maximum number of peaks that can be separated in a given analysis, is the most common metric of separation power in gradient chromatography. However, due to the extreme complexity of many biological samples, most detected components are highly overlapped with other components. The best way to reduce the degree of overlap is to increase the peak capacity of the separation. Therefore, my research is mainly focusing on the following areas: (1) To develop a theoretical framework for peak capacity optimization in one-dimensional separation of peptides. We study the effect of gradient time, flow rate, temperature and final eluent strength on the peak capacity of tryptic digest peptide separations. Due to the strong interactions between the individual variables (e.g. flow rate and gradient time), peak capacity optimization is quite complicated. To address this problem, we develop an easily implemented, highly efficient and effective Monte Carlo search strategy to simultaneously optimize all the variables. (2) To obtain highest peak capacity on conventional instruments for proteomic research in a reasonable amount of time. We devise a mixture of eleven commercially available peptides which is representative of typical peptides from protein tryptic digestion. We also compare different types of stationary phase in peptides separations (pellicular vs. totally porous). By using a long column set packed with 5 micron pellicular stationary phases, we obtain record high peak capacities of > 500 in two hours with pressure drops less than 400 bar. (3) To optimize the peak capacity of fast, comprehensive two-dimensional liquid chromatography (2DLC). In the 2DLC system, we use sub-minute gradient high-temperature LC as the second dimension to reduce the total analysis time to 30 – 60 minutes. We study the peak capacity production optimization in the second dimension and predict the best analysis time of the second dimension. We analyze complex proteomic or metabolomic samples using the optimized 2DLC to demonstrate its ability in handling extremely complicated mixtures in a shorter analysis time compared with conventional ambient temperature 2DLC.
2. Methodology for Development of More "Universal" Chiral Stationary Phases – The "Double Reciprocal" Hypothesis During the last two decades, hundreds of Chiral Stationary Phases (CSPs) for HPLC separation of enantiomers have been developed and commercialized; however, in most cases, a given CSP is only able to separate a narrow range of compounds and the trial and error search for the best CSP for a given separation is tedious. It would be very desirable to develop a small number of more or less "universal" CSPs capable of separating a wide variety of chiral compounds. In order to design more universal CSPs, we propose a novel double reciprocal concept inspired by Pirkle's reciprocal concept. To choose the most universal selector from a set of promising molecules target candidate species denoted T 1 – T m, we first separate their racemic mixtures of the targets on a series of highly variegated commercial CSPs. The best separated selector (T best) is taken as that which can be acceptably separated on the largest number of commercial CSPs with the highest average enantioselectivity. Based on our "double reciprocal" concept, we propose that the CSPT best, prepared by immobilizing enantiomerically pure T best on chromatographic support, will provide enantioselectivities toward the widest variety of chiral analytes. To gain some theoretical support for our double reciprocal concept before attempting its experimental test, we used a simple statistical thermodynamic model which is an extension of the work of Martire et al., which allows us to compute enantioselectivities of different analytes on different CSPs. This model was tested and validated by comparing it to Pirkle's reciprocal concept with which it is consistent and based on this model we have theoretically validated the double reciprocal hypothesis.
RECENT PUBLICATIONS
PRESENTATIONS (* Presenter)
Last updated: 01/2006 |
