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August/September 2011
apart on the surface. This approach, provided by SIELC’s Obelisc N columns, has both ion-exchange functionalities (cation and anion-exchange) combined, but spaced far apart. Strongly basic and strongly acidic groups are separated by long hydrophilic chain, which makes these ionisable groups available for both ion-exchange interactions (Figure 15).
Conclusions
Figure 15. Effect of both pH and organic content. on a separation of sugars, amino acids, and carboxylic acids
the mobile phase should be above 5. Bare- silica HILIC columns suffer from non- uniformity of the surface in terms of cation-exchange properties due to mentioned before inclusions, and aminopropyl column suffer from stability issues. Sequant managed to overcome these stability and non-uniformity issues by developing zwitter-ionic stationary phase [11]. Presence of ionised quaternary amino and sulphonates groups guarantees a very polar uniform surface. However both groups are closely positioned to each other, making the ion exchange mechanism almost impossible to achieve. In order to observe additional selectivity, for example, by ion- exchange mechanism, two appositely charged groups should be placed farther
Modern mixed-mode columns offer great flexibility, reproducibility, and loadability for separation of a wide range of compounds. These columns can be employed in multiple and single modes, and can be used to develop reversed-phase, ion-exchange, ion- exclusion and HILIC methods. All modern mixed-mode columns are compatible with LC/MS and prep chromatography, and can be used to successfully develop methods in pharmaceutical, chemical, food, and environmental tasks.
Method development in mixed-mode chromatography is based on understanding of individual interactions -- hydrophobic, HILIC, and ionic -- working together.
Notes
Acclaim is a trade mark of Dionex Corporation. Scherzo is a trademark of Imtakt. Chromatograms are courtesy of Dionex and Imtakt.
References
1.www.acdlabs.com/products/adh/ chrom/chrom_apps_db/
2.www.sielc.com/
MethodDevelopment_Guide.html
3.www.sielc.com/
MethodDevelopment_CompoundType.html
4. Lämmerhofer M, Richter M, Wu J, Nogueira R, Bicker W, Lindner W., J.
Sep.Sci 2008, Vol. 31, 2572-2588.
5. Liu, X., Pohl, C., American Laboratory, 2007, Vol. 39, 2572-2588.
6. McCalley, D., J. of Chromatography A, 2010, Vol. 1217, 858-880.
7. Fekkes, D., Van Dalen, A., Edelman, M., Voskuilen, A., J. of Chromatography B, 1995, Vol. 669, 177-186.
8. Chaimbault, P., Petritis, K., Elfakir, C., J. of Chromatography A, 1999, Vol. 885, 191-202.
9.Waksmundzka-Hajnos, M., J. of Chromtography B, 1998, Vol. 717, 93-118.
10. Olsen,B., J. of Chromatography A, Vol. 913, 113-122.
11. Hemstrom, P., Irgum, K., J. of Sep. Sci., 2006, Vol. 29, 177-181.
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HPTLC Hyphenation For Speed & Precision
There are times when more analytical information is required than HPTLC alone can provide. Swiss Planar Chromatography instrument manufacturer, CAMAG, is at the forefront of HPTLC hyphenation. UK distributor, Omicron Research Limited, brings you CAMAG’s CBS106 magazine, comprising international studies demonstrating this capability. Hyphenation of HPTLC can take many forms, combining HPTLC with diode array detectors, evaporative light scattering detectors, polarimetric detectors or circular dichroism detectors. Use of CAMAG’s Bioluminizer interface combines the separation power of planar chromatography with bioluminescence detection, enabling the identification of single biologically active compounds, as revealed in an article on antibiotics in milk. CAMAG’s TLC-MS proves its worth when fingerprinting herbal essential oils. This interface allows rapid elution of TLC/HPTLC zones with online transfer to any HPLC/MS system without modification. Within seconds a substance’s mass spectrum can be determined in this way. This edition of CAMAG’s Bibliography Service include papers on Traditional Chinese Medicine, peptides from tryptic protein digest and sucralose in water.
Contact Omicron for your free copy of CBS 106:
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