Medical Physics Research Today is a free monthly online journal that collates and summarizes the latest research about Medical Physics, including details on medicine, radiotherapy, biomechanics, medical imaging. | ||||||||
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Single-run separation of cationic, anionic, and polyanionic compounds by CE-ESI-MS.Mokaddem M, Varenne A, Belgaied JE, Factor C, Gareil P Laboratoire d'Electrochimie et Chimie Analytique, UMR 7575 CNRS-ENSCP-Paris 6, Paris, France. A method for a single-run separation of cationic, anionic, and polyanionic compounds by CE hyphenated to ESI MS (CE-ESI-MS) is described. One of the main issues for coupling CE to MS with an ESI source consists in maintaining an electric contact for the electrophoretic separation. This condition is only performed if a liquid flow arising from the separation capillary is directed to the needle, making it coupling-compatible. This latter situation is incompatible with the separations of polyanionic compounds of higher electrophoretic mobility (in absolute value) than the electroosmotic mobility, performed in bare fused-silica capillaries under a negative polarity. In this study, several alternative approaches were evaluated to circumvent this difficulty, and applied to the setup of the CE-MS separation of a mixture containing both cationic and polyanionic compounds, which are synthesis intermediates of contrast agents for medical imaging. Eventually, the detection of the cationic and anionic compounds in a single run could be obtained by either using neutrally coated polymethylsiloxane (DB-1) capillaries and simultaneously applying a negative voltage polarity and a pressure allowing to compensate for the residual cathodic EOF or by dynamically modifying the inner wall of a bare fused-silica capillary with a polycationic polymer (hexadimethrine bromide) and using it afterwards under negative voltage polarity. Published 3 September 2007 in Electrophoresis, 28(17): 3070-7.
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