Solid-state I3C NMR spectra of "N-containing compounds obtained under CPMAS conditions often show asymmetric doublets arising from the unaveraged l3C,l4N residual dipolar coupling. A similar result has recently been noticed in deuteriated samples, whose "C resonances showed the combined effect of %,*H dipolar and scalar couplings. A simple approach, easily adaptable to a desk microcomputer, is described for simulating "C line shapes for arbitrary values of quadrupole parameters, C-X (X = I4N, 'H) distances, external field and orientation of the internuclear vector in the axis system where the electric field gradient tensor is diagonal.

An on-line affinity selection method using a polymeric monolithic support is proposed for the retention of histidine-containing peptides and their subsequent separation by capillary zone electrophoresis (CZE). Monolithic capillary columns were prepared in fused-silica capillaries of 150 mum inner diameter (ID) by ionizing radiation-initiated in situ polymerization and cross-linking of diethylene glycol dimethacrylate and glycidyl methacrylate, and chemically modified with iminodiacetic acid (IDA) and copper ion. Monolithic microextractors were coupled on-line near the inlet of the separation capillary (fused-silica capillary, 75 mum ID x 28 cm from the microextractor to the detector). Model peptide mixtures of histidine-containing and histidine-noncontaining peptides were assessed. Peptides were released from the sorbent by a 5 mM imidazole solution and then separated by CZE with ultraviolet detection. Relative standard deviation values for migration times and corrected peak areas were found to be lower than 5.8 and 10.5%, respectively. IDA-Cu(II) ion modified monolithic microextractors showed a chromatographic behavior and could be reused at least 25 times. The use of monolithic supports proved to be an advantageous alternative to packed particles for the preparation of microextractors.

No abstract

No abstract