May 2007 Meeting

Geometry of HPLC Adsorbents
Surface area of chemically modified silica.
Surface-specific versus volume-specific retention.

The May 2007 CSSC meeting will be held at the Yankee Silversmith Inn in Wallingford, CT.  The meeting will feature a technical presentation by Dr.Yuri Kazakevich of Seton Hall University, as well as hors d'oeuvres and a cash bar.  The cost of the meeting is $25 ($15 Students and Emeritus) and is to be paid at the event.

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Abstract:  It is generally well known that HPLC retention of any analyte is proportional to the available adsorbent surface area. On the other hand, all commonly used retention descriptors do not account for that parameter. Pore volume (Vp), pore diameter (Dp), and surface area (S) are three main characteristics of adsorbent geometry. Cylindrical pore model is generally assumed to be applicable, which leads to the following relationship:

K.K. Unger found 15 to 20% deviation of experimental data from this relationship for large number of different adsorbents he verified. Pore volume for most modern HPLC adsorbents are within 0.8 to 1.2 mL/g, while their surface area could vary from 100 to 500 m2/g. There is approximately 1 g of adsorbent in 150x4.6 mm column with 65 to 70% of its volume occupied by adsorbent particles. This results in only 1.5 to 1.9 mL of void volume variation. The use of surface-specific retention parameters allow for better column-to-column comparison and it reflect real analyte – surface interactions.
Reversed-phase adsorbents are silica-based materials with chemically modified surface. This modification alters not only chemical properties of the surface but also its geometry. The assessment of the geometry variation for modified silica will be discussed in the direction of comparison of different columns.
Eluent component adsorption isotherms on the surface of chemically modified silicas will be discussed from the point of view of adsorbed layer formation and assessment of the relative amount of accessible residual silanoles.

Biography:  Dr. Yuri Kazakevich is an Associate Professor of Chemistry at Seton Hall University with thirty years of experience in liquid chromatography. He has over fifteen years of academic research experience in Russia and fifteen years of research, teaching and consulting for major American pharmaceutical companies, which has resulted in numerous papers, four book chapters and recent opus magnum – “HPLC for Pharmaceutical Scientists” – comprehensive book on HPLC theory, methodology and applications in pharmaceutical industry, published by Wiley.

The main focus of Dr. Kazakevich research is HPLC retention mechanisms and the description of the analyte migration through the column with emphasis on the influence of adsorbent geometry and the surface chemistry. Dr. Kazakevich is also the author of the oldest and most complete online instructional resource – “Basic Liquid Chromatography” web-book.

Yankee Silversmith Inn
1033 North Colony Road
Wallingford, CT 06492
(203) 269-5444

Last Updated:  08/15/2007 09:53 AM