Monolithic columns with a gradient of functionalities prepared via photoinitiated grafting for separations using capillary electrochromatography

Abstract

Stationary 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.

Mechanically Tunable Thin Films of Photosensitive Artificial Proteins: Preparation and Characterization by Nanoindentation

“…40 While step gradients are easy to characterize with a limited number of indentations, films with smooth gradients of elastic modulus could also be made via the variable irradiation approach by moving an opaque shutter continuously across the film. 41 Gradients could be implemented over a variety of length scales. The spatial resolution of the modulus measurement is limited only by the 300 nm radius of the tip used for indentation, and is adequate for measurement of the variation in mechanical properties under a single spread cell.…”

Monolithic Materials: Promises, Challenges, Achievements

“…The photolithographic approach also enabled the preparation of capillaries for on-line adsorption of selected proteins, on the basis of their affinity for immobilized copper ions or ion exchange functionalities, followed by electrophoretic separation (37 ). In a similar approach, a moving shutter or a stepped-density mask was used to graft the pore surface with longitudinal gradients of chemistries (38). Layers of different chemistries were achieved by consecutive grafting of different monomers on top of each other.…”

Evaluation of photografted charged sites within polymer monoliths in capillary columns using contactless conductivity detection

“…The same approach was used in this work, but in this case ionisable functional monomers were photo-grafted onto a butyl methacrylate monolith using techniques previously discussed. AMPS was selected as a suitable candidate for grafting since it contains a strong acid sulphonate group which is ionised across the pH range, and because the grafting of this monomer onto polymer monoliths has been well studied [1,2]. Figure 3 shows the C 4 D profile of a butyl methacrylate monolith containing two zones of photografted AMPS.…”

“…A number of recent publications [1][2][3][4] have demonstrated the use of photografting methodologies for the modification of pre-formed monolithic stationary phases. Essentially, this procedure involves filling the pores of a monolith with a functional monomer in the presence of a free radical initiator and an inert solvent.…”