174 research outputs found
Aqueous normal phase retention of nucleotides on silica hydride-based columns: Method development strategies for analytes revelant in clinical analysis
No full textAn aqueous normal phase HPLC method coupled with UV or ESI/MS detection was used for the determination of a wide variety of nucleotides, essential in metabolomics studies. Fifteen nucleotides were tested in clinically relevant mixtures at levels of 100 g/mL for UV detection and 1 g/mL for ESI-MS detection. Analysis times for all protocols developed were less than 20 min. The chromatographic conditions were changed to achieve optimized retention and separation of the nucleotides studied. The aqueous normal phase-HPLC methods were developed utilizing two columns, one having a minimally modified hydride surface another having an undecanoic acid moiety on a hydride surface. Volatile, low ionic strength mobile phases were used. Negative ion mode ESI-MS at near neutral pH mobile phase, combined with a TOF detector provided a highly sensitive and specific method, which is equally suitable for quadrupole and ion trap instruments. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Monolithic columns with a gradient of functionalities prepared via photoinitiated grafting for separations using capillary electrochromatography
No full textStationary phases for capillary electrochromatography with a longitudinal gradient of functionalities have been prepared via photoinitiated grafting of polymer chains onto the pore surface of a porous polymer monolith. In order to achieve the desired retention
and electroosmotic flow, the hydrophobic poly(butyl methacrylate-co-ethylene dimethacrylate) monolith with optimized porous properties was grafted with a layer of ionizable polymer, poly(2-acrylamido-2-methyl-1-propanesulfonic acid). A moving shutter and a neutral density filter were used to control the dose of UV light received at different locations along the monolith in order to create the longitudinal gradient of functionalities. Formation of the desired gradients was confirmed using electron probe microanalysis of different locations along the column. The preparation technique
significantly affects performance in the CEC mode as demonstrated on the separations of a model mixture using columns both with homogeneous distribution of grafts and with a gradient of functionality. Columns grafted with the gradient of functionalities
were found superior to those functionalized uniformly. A comparison of the performance of the gradient column with another containing evenly distributed functionalities showed the performance benefits of the “gradient” column
Quest for organic polymer-based monolithic columns affording enhanced efficiency in high performance liquid chromatography separations of small molecules in isocratic mode
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