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Analytical Separation Science and Technology

We have built a strong and highly interconnected research profile around the basic understanding of analytical methods, ranging from the mechanisms of analyte-surface interactions to macroscale transport. This approach relies on the discovery of the fundamental morphology–functionality–transport relationships and requires (i) modern simulation methods to capture the involved widely different spatio-temporal scales, and (ii) the precise physical reconstruction of the involved porous media. A variety of experimental chromatographic techniques (microchip and capillary HPLC, analytical chromatography) are used to complement the modeled data, but also to explore their integration onto miniaturized platforms and identify performance limitations in current practice. Experimental investigations include

(i) the characterization and optimization of microchip HPLC using particle-packed microfluidic channels with non-cylindrical conduit geometries,
(ii) on-line coupling of microchip electrospray with mass spectrometric detection,
(iii) the demonstration of high-efficiency, meter-long capillary ultrahigh pressure liquid chromatography columns, and
(iv) silica-based packings and monoliths with (sub)micrometer macropores for use as efficient narrow-bore and analytical-format HPLC columns.

Figure: Ulrich Tallarek
Figure 1: Layout of polyimide HPLC/MS chips integrating sample enrichment, HPLC separation on a packed particulate bed, and electrospray ionisation. Enlargements show details of the chip: a) six-port-interface and serpentine enrichment column, b) µ-sieves for retaining the packing at the inlet of enrichment and separation columns, and c) and d) the ESI-tip with its gaussian-shaped orifice. Two internally grounded electrodes provide the contact to the microfluidic channel near the ESI-tip (see electrical interface).

Figure: Ulrich Tallarek

Figure 2: a) SEM image of the ca. 50 µm (height) × 75 µm (median) trapezoidal cross-section of the separation column. The packed bed contains 5 µm Zorbax SB-C18 particles at an interparticle porosity of ~0.42. b) Microfabricated channels act as µ-frit to retain the packing at the outlet of the separation column.

Figure: Ulrich Tallarek

Figure 3: Separation efficiency (plots of pleight height H vs. average mobile phase velocity) for particle-packed microchannels with non-cylindrical cross-sectional geometry. (Left panel) Trapezoidal channels packed with 5-µm particles. With improved packing conditions the interparticle porosity decreases from 0.47 to 0.42. (Right panel) Comparison of plate height curves for different microchannels (trapezoidal, quadratic, or gaussian conduit shape) packed with 3-µm and 5-µm particles.

Highlighted publications:

  • A.E. Reising, J.M. Godinho, J.W. Jorgenson, U. Tallarek
    Bed morphological features associated with an optimal slurry concentration for reproducible preparation of efficient capillary ultrahigh pressure liquid chromatography columns.

    Journal of Chromatography A
    2017, 1504, 71–82. DOI: 10.1016/j.chroma.2017.05.007
  • J.M. Godinho, A.E. Reising, U. Tallarek, J.W. Jorgenson
    Implementation of high slurry concentration and sonication to pack high-efficiency, meter-long capillary ultrahigh pressure liquid chromatography columns.

    Journal of Chromatography A
    2016, 1462, 165–169. DOI: 10.1016/j.chroma.2016.08.002
  • K. Hormann, U. Tallarek
    Mass transport properties of second generation silica monoliths with mean mesopore size from 5 to 25 nm.

    Journal of Chromatography A
    2014, 1365, 94–105. DOI: 10.1016/j.chroma.2014.09.004
  • K. Hormann, T. Müllner, S. Bruns, A. Höltzel, U. Tallarek
    Morphology and separation efficiency of a new generation of analytical silica monoliths.

    Journal of Chromatography A
    2012, 1222, 46–58. DOI: 10.1016/j.chroma.2011.12.008
  • S. Jung, U. Effelsberg, U. Tallarek
    Microchip electrospray: Improvements in spray and signal stability during gradient elution by an inverted post-column make-up flow.

    Analytical Chemistry
    2011, 83, 9167–9173. DOI: 10.1021/ac202413z
  • S. Ehlert, L. Trojer, M. Vollmer, T. van de Goor, U. Tallarek
    Performance of HPLC/MS microchips in isocratic and radient elution modes
    Journal of Mass Spectrometry
    2010, 45, 313–320. DOI: 10.1002/jms.1719
  • S. Jung, A. Höltzel, S. Ehlert, J.-A. Mora, K. Kraiczek, M. Dittmann, G.P. Rozing, U. Tallarek
    Impact of conduit geometry on the performance of typical particulate microchip packings.

    Analytical Chemistry
    2009, 81, 10193–10200. DOI: 10.1021/ac902069x