Ted Szczerba

Abbott Laboratories, North Chicago, IL, United States

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Publications (6)19.43 Total impact

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    ABSTRACT: With the aim of exploring the potential of ultra-fast chiral chromatography for high-throughput analysis, the new sub-2 micron Whelk-O 1 chiral stationary phase (CSP) has been employed in supercritical fluid conditions to screen 129 racemates, mainly of pharmaceutical interest. By using a 5-cm long column (0.46cm internal diameter), a single co-solvent (MeOH) and a 7-min gradient elution, 85% of acidic and neutral analytes considered in this work have been successfully resolved, with resolution (Rs) larger than 2 in more than 65% of cases. Moreover, almost a half of basic samples that, for their own characteristics, are known to be difficult to separate on Whelk-O 1 CSP, have shown Rs greater than 0.3. The screening of the entire library could be accomplished in less than 24h (single run) with 63% of positive score. For well-resolved enantiomers (Rs roughly included between 1 and 3), we show that method transfer from gradient to isocratic conditions is straightforward. In many cases, isocratic ultra-fast separations (with analysis time smaller than 60s) have been achieved by simply employing, as isocratic mobile phase, the eluent composition at which the second enantiomer was eluted in gradient mode. By considering the extension and variety of the library in terms of chemico-physical and structural properties of compounds and numerousness, we believe that this work demonstrates the real potential of the technique for high-throughput enantioselective screening. Copyright © 2015. Published by Elsevier B.V.
    No preview · Article · Jan 2015 · Journal of Chromatography A
  • Gregory K Webster · Ted J Szczerba
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    ABSTRACT: The majority of enantiomeric separations for purity analysis and quality control continue to be performed by normal-phase liquid chromatography and supercritical fluid chromatography. In this chapter, representative chromatographic screening procedures for the enantioseparations using Pirkle-type stationary phases are presented. As Pirkle-type phases are commonly applied to the preparative chromatographic isolation of enantiomers, volatile modifiers are used in this screen in order to be subsequently compatible with the techniques used to recover analytes from preparative scale isolations.The Stage 1 screen presented here is used initially for screening chiral entities. The gradients use cyclohexane and ethanol both with and without chromatographic modifiers. The Stage 2 screen is used for more challenging to resolve compounds that do not exhibit resolution using the Stage 1 screening procedure.
    No preview · Article · Jan 2013 · Methods in molecular biology (Clifton, N.J.)
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    ABSTRACT: This paper reports on the thermodynamic and kinetic evaluation of a new ultra-high performance liquid chromatography broad-spectrum Pirkle-type chiral stationary phase (CSP) for enantioselective applications (eUHPLC). The well-known Whelk-O1 selector was covalently immobilized onto 1.7-μm high-surface-area, porous spherical silica particles to produce a totally synthetic, covalently bonded CSP that was packed into 150mm, 100mm, 75mm and 50mm columns, either 4.6 or 3.0mm ID. A 100mm×4.6mm ID column was fully characterized from a kinetic and thermodynamic point of view, using as reference a conventional HPLC Whelk-O1 column, 250mm×4.6mm ID, based on 5-μm porous silica particles. On the eUHPLC column, van Deemter plots generated H(min) values of 3.53μm for 1,3-dinitrobenzene, at an interstitial mobile phase linear velocity (μ(inter)) of 5.07mm/s, and H(min) of 4.26 and 4.17μm for the two enantiomers of acenaphthenol, at μ(inter) of 4.85mm/s and 4.24mm/s, respectively. Resolution of 21 enantiomeric pairs including alcohols, epoxides, sulfoxides, phosphine oxides, benzodiazepines and 2-aryloxyproprionic esters used as herbicides, were obtained with significant advantages in terms of efficiency and analysis time. Speed gain factors were calculated for the different column geometries (150mm, 100mm, 75mm and 50mm, either 4.6 or 3.0mm ID), with respect to the standard HPLC column (250mm×4.6mm ID), and were as high as 13, in the case of the 50-mm-long column, affording sub-minute separations of enantiomers with excellent resolution factors. In particular, trans-stilbene oxide was resolved in only 10s, while a 50mm×3.0mm ID column was used as a compromise between reduced mobile phase consumption (less than 1mL per analysis) and smaller extra-column band-broadening effect. Given the relatively low viscosity in NP mode, and the excellent permeability of these eUHPLC columns, with backpressure values under 600bar for a wide range of flow rates, the use of standard HPLC hardware is possible. In this case, however, a significant loss in resolution is observed, compared to the UHPLC instrumentation, if no modifications are introduced in the HPLC apparatus to reduce extra-column variance. The excellent efficiency and selectivity, conjugated with the very high-throughput and the ultra-fast analysis time, prove the potentials of the eUHPLC Whelk-O1 columns in the development of enantioselective UHPLC methods.
    No preview · Article · Sep 2012 · Journal of Chromatography A
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    ABSTRACT: A new chiral stationary phase for ultrahigh-pressure liquid chromatography (UHPLC) applications was prepared by covalent attachment of the Whelk-O1 selector to spherical, high-surface-area 1.7-μm porous silica particles. Columns of varying dimensions (lengths of 50, 75, 100, and 150 mm and internal diameters of 3.0 or 4.6 mm) were packed and characterized in terms of permeability, efficiency, retention, and enantioselectivity, using both organic and water-rich mobile phases. A conventional HPLC Whelk-O1 column based on 5.0-μm porous silica particles and packed in a 250 mm × 4.6 mm column was used as a reference. Van Deemter curves, generated with low-molecular-weight solutes on a 100 mm × 4.6 mm column packed with the 1.7-μm particles, showed H(min) (μm) and μ(opt) (mm/s) values of 4.10 and 5.22 under normal-phase and 3.74 and 4.34 under reversed-phase elution conditions. The flat C term of the van Deemter curves observed with the 1.7-μm particles allowed the use of higher-than-optimal flow rates without significant efficiency loss. Kinetic plots constructed from van Deemter data confirmed the ability of the column packed with the 1.7-μm particles to afford subminute separations with good efficiency and its superior performances in the high-speed regime, compared to the column packed with 5.0-μm particles. Resolutions in the time scale of seconds were obtained using a 50-mm-long column in the normal phase or polar organic mode. The intrinsic kinetic performances of 1.7-μm silica particles are retained in the Whelk-O1 chiral stationary phase, clearly demonstrating the potentials of enantioselective UHPLC in terms of high speed, throughput, and resolution.
    No preview · Article · Jun 2012 · Analytical Chemistry
  • C.J. Welch · T. Szczerba
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    ABSTRACT: Chromatographic separations of the enantiomers of several commercial agricultural compounds on the Whelk-O chiral stationary phase are reported. The analytes examined include herbicides, fungicides, insecticides and insect pheromones. Most of the resolutions are of sufficient quality for chromatographic determination of enantiomeric purity, and several are suitable for large scale preparation of pure enantiomers.
    No preview · Article · Jan 1998 · Enantiomer A Journal of Stereochemistry
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    ABSTRACT: The Whelk-O 1 chiral stationary phase is generally useful for the chromatographic separation of the enantiomers of many classes of analytes including aryl propionic acid non-steroidal anti-inflammatory drugs, aryl epoxides, sulfoxides, alcohols, amides and esters. We herein report some additional recent enantioseparations obtained with this column, including a number of pharmaceuticals such as thalidomide, nicardipine, isradipine, mephenytoin, nirvanol, cyclandelate, bendroflumethiazide, bupivicaine, tolperisone, proglumide, tropicamide and indapamide. The separation of the enantiomers of a collection of additional analytes is also reported, including several compounds containing basic nitrogen, a heretofore difficult class of compounds to resolve with this column.
    No preview · Article · Jan 1997 · Journal of Chromatography A