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Tuesday, February 21, 2012
Mark Schure: What is separation orthogonality and how do you measure it? Designing and Optimizing Separations
Mark Schure
Dow
Spring House, PA
Abstract:
It has long been understood that using multidimensional separation schemes increases the chances of resolving fused peaks by increasing the separation space and by providing a different separation mechanism to spread zones out over an area (instead of a line as in one-dimensional chromatography). Some people like to think of this as a multiplicative increase in peak capacity, i.e. the ability to put many more peaks into an area instead of a line-like chromatogram. This is much easier said than done (actions speak louder than words!) because there is a certain element of randomness to chromatograms. Therefore peaks can never be lined up into rectangular-spaced domains in two dimensions, no matter how clever the choice of gradient elution conditions.
For very complex separations, for example separating hydrocarbon mixtures like diesel fuel, there is just too much saturation in a one-dimensional chromatogram and one is forced to use multidimensional techniques. However, if the separation mechanism is similar between the two columns used in a twodimensional separation, the gain in resolution may not be worth the effort because the peaks will line up on the separation diagonal and one column would give similar results.
The term “orthogonality” usually refers to the statistical concept of spreading peaks across a twodimensional chromatogram. However, this concept can be generalized to a one-dimensional chromatogram (spreading peaks across a line chromatogram), and three-dimensional chromatograms (spreading the peaks across a volume or three dimensions), etc. One of the challenges in two-dimensional chromatography is picking the two columns that are used. There are many column pairs that have been previously used that include reversed-phase, ion exchange, size exclusion, normal-phase, and a host of other special phases. But how does one measure this elusive quantity orthogonality?
One method that was proposed1 is to utilize the fractal dimension or more rigorously the Hausdorf dimension. I call this the dimensionality of the separation. This method has a number of advantages:
1) It is dimensionally-invariant, i.e. it works for 1D, 2D, and any number of dimensions.
2) It is scale-invariant; it doesn’t matter if the chromatographic run time is seconds, minutes or hours or a mixture for multidimensional separations.
3) It is relatively easy to calculate.
4) It has easily understandable limits that appeal intuitively to chromatographers.
In this talk dimensionality as a measure of separation orthogonality will be discussed. Common examples with experimental1 and synthetic chromatograms1,2 will be illustrated. I will also explain other methods for measuring separation orthogonality that have appeared in the literature and contrast their advantages and disadvantages.
1Schure, M. R., The dimensionality of chromatographic separations, J. Chromatogr. A, 2011, 1218, 293-
2Schure, M. R., Davis, J. M., The statistical overlap theory of chromatography for power-law (fractal) statistics, J. Chromatogr. A, in press.
About the Speaker:
Mark R. Schure received his undergraduate education at Northeastern University (Boston, MA) and received his Ph.D. in atmospheric chemistry from Colorado State University. Following two!years of post-doctoral study at the University of Utah with Prof. J. Calvin Giddings, he entered industry in the science group at Digital Equipment Corporation in Marlborough, Massachusetts in 1984. In 1989, Mark moved to the Computational Chemistry group at the Rohm and Haas Company (now The Dow Chemical Company), where he is a Distinguished Scientist.
Mark’s research interests are in the fundamental separation science of complex molecules, polymers and colloids, molecular modeling of fluid phases, colloid and materials chemistry, and solving large-scale chemical and physical problems with computers. He received the Arthur Doolittle award from the PMSE (Polymeric Materials Science and Engineering) Division of the ACS in 1991 and the Northeastern University Distinguished Alumni in Chemistry award in 1993. He received the Douglas Leng award within The Dow Chemical Company for basic research in Engineering Sciences in 2011.
Since 1995 Mark has been an Adjunct Professor of Chemical Engineering at the University of Delaware. He was symposium chairman of the HPLC 2004 conference in Philadelphia and has been cochairman of the ISPPP (International Symposium on the Separation of Proteins, Peptides and Polynucleotides) conference series in the United States. He has published over 100 papers, has four patents, and recently edited the book Multidimensional Liquid Chromatography in 2009.
Details:
| Location: | D'ignazio's Towne House |
| Times: | 5:00 PM Executive Committee Meeting 5:45 PM Social "Hour" 6:30 PM Dinner 7:30 PM Presentation |
| Cost: | $30 |
| Dinner Choices: | Veal parmesan Flounder stuffed with crabmeat Eggplant parmesan |
NOTICE TO STUDENTS AND FACULTY: Full-time students with valid ID may attend dinner meetings at half-price. Faculty members at colleges and universities are urged to bring one or more students to the meeting. If they do, they also can attend at half-price.