Stepped gradients on polymeric monolithic columns by photoinitiated grafting

Abstract

The surface of polymethacrylate monoliths was functionalized by a post-polymerization modification, by means of a novel photo-initiated graft procedure where the charged monomer, sulfopropyl methacrylate, was controllably grafted stepwise, i.e. with incremental graft energies. The grafting approach was optimized using scanning capacitively coupled contactless conductivity detection. The effect of the localized ion exchange capacity and resultant gradient stationary phase upon ion-exchange chromatographic retention, selectivity, and performance was investigated, and compared to a homogeneously grafted (isotropic) column. The gradient column provided reduced peak widths at half height for both cationic analytes, with a reduction of 34 and 33%, respectively, when compared to the isotropic column.

Monolithic stationary phases with a longitudinal gradient of porosity

“…It should be pointed out, however, that these conclusions are based on inverse SEC data only. Other characterization techniques, such as high resolution field emission SEM or contactless conductivity detection might provide more insight into the pore volume distribution of hypercrosslinked columns.…”

“…The second column was divided in three equal sections (8.3 mm each) that were hypercrosslinked for 120, 240, and 360 min. It should be noted that in the frame of this short communication we did not further characterized homogeneity of single columns with the gradient of porosity . Both completely hypercrosslinked columns as well as columns with the gradient of porosity were first flushed with water and then with the mobile phase.…”

“…Covalent immobilization of ampholytes distributed along the column length was used for the preparation of monolithic column with gradient of pH functionality . Photoinitiated surface grafting offers full control over the surface chemistry and allows formation of longitudinal gradient of functionality . Monolithic thin layers with a diagonal gradient of hydrophobicity was also prepared and used in 2D TLC separations .…”

Contactless conductivity detection for analytical techniques— Developments from 2014 to 2016

“…C 4 D is predominantly used in CE and MCE (see the former sections), but conductivity measurements are also useful for various other flow‐through analytical techniques, including LC, capillary LC, flow/sequential injection analysis and in microfluidic platforms. In the reviewed period, several publications on C 4 D in IC , open‐tubular IC , capillary IC and standard LC were reported. A reversed phase isocratic LC method was optimized for determination of aminoglycosidic antibiotics, which lack UV‐absorbing chromophores and are thus not suitable for LC analyses with conventional UV‐Vis absorbance detection .…”

“…In this procedure, the detector is moved in discrete steps along the length of the column for repeated measurements. Scanning C 4 D was also applied for characterization of polymethacrylate monoliths . The monoliths were functionalized by a photo‐initiated stepwise grafting procedure and the effect of the stepwise grafting (compared to homogeneous grafting) was subsequently examined by IC analysis of barium and magnesium with on‐column C 4 D. Another application of scanning C 4 D was reported for characterization of porous open‐tubular layers of polystyrene‐divinyl benzene bonded onto walls of fused silica photonic crystal fibers (FS‐PCFs) .…”