Application of the Retention Index Concept in Micellar Electrokinetic Capillary Chromatography. [Erratum to document cited in CA120:123851]

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The separation of herbicides by micellar electrokinetic capillary chromatography

A method for the sepn. of a no. of herbicides consisting of chlorophenoxy acids by micellar electrokinetic capillary chromatog. (MECC) was developed. SDS, Brij 35, cetyltrimethylammonium bromide (CTAB) and MeOH were introduced into the buffers to investigate their effects on the sepn. of the herbicides. SDS combined with Brij 35 as the micellar agent was found to provide the best overall sepn. of these component

Novel, intramolecular hydrogen-transfer and cyclo-addition photochemistry of cyclic 1,3-dienes

With use of one- and two-dimensional NMR spectroscopy and deuterium labelling, the photochemistry of 9-endo-hydroxy-9-exo-vinyl-bicyclo[4.2.1]nonadiene (1) and the 9-exo-(11-dimethylvinyl)- (2) and 9-exo-ethyl- (3) analogues has been studied. Irradiation of 1–3 gave novel 8-membered ring systems 4–6 by a light-induced rearrangement process, in which the hydroxyl proton is transferred on one side of the molecule toward one of the termini of the endocyclic diene. This rearrangement process thus involves a formal hydrogen transfer, during which either H+ or H• may be transferred to a reactive diene intermediate. Replacement of the hydroxyl proton by deuterium in 1–3, and 2H NMR of the corresponding photoproducts, confirmed that the hydrogen translocation occurs intramolecularly. Prolonged irradiation of 4 and 5 results in the formation of pyran products 10 and 11 by an intramolecular photocycloaddition of the triplet excited state of the a,ß-unsaturated ketone to 1,3-cis,cis-cyclooctadiene, via a stabilized bisallylic biradical intermediate. Conformational studies of the structurally more rigid system 10, which is derived from 4, revealed that the hydroxyl proton was transferred on the endo side of the molecul

Application of the Retention Index Concept in Micellar Electrokinetic Capillary Chromatography

The application of the retention index concept in micellar electrokinetic capillary chromatog. (MECC) was evaluated for the identification of neutral species. Homologous series of alkylbenzenes and alkylaryl ketones were applied as retention index stds. and also for the calcn. of the micelle migration time by an iteration procedure. The relation between retention indexes, I, and octanol-H2O partition coeffs. is discussed, and DI values were calcd. from retention indexes, obtained with both anionic and cationic surfactant systems, to study the sepn. mechanism for solutes with different functionalities in MECC. The influence of the phase ratio is treated theor., and the capacity factor is linearly related to the surfactant concn., whereas the retention index is independent of the surfactant concn. The temp. dependence of the retention index was studied and the std. enthalpy, entropy, and Gibbs free energy for micellar solubilization of the sample compds. were detd., showing that the hydrophobic interaction plays a significant role in MECC ana

Comparison of spherically and irregularly shaped stationary phase packings in microcolumn liquid chromatography

Spherically and irregularly shaped reversed phase packings were used to slurry pack capillary fused silica columns. The selection of the packing solvents was based on the colloidal properties of the stationary phase particles and investigated by sedimentation experiments. The chromatographic performance of the microcolumns was measured with conventional parameters from plate and rate theories, and the column resistance parameter and separation impedance. Also studied was the time of analysis. The performance of spherical and irregular packings was comparable with a light preference for spherically shaped materials when time of analysis is concerned

29Si NMR Model Dissolution Study of the Degradation of Reversed Phases for High-Performance Liquid Chromatography

To simulate aging under chromatog. conditions, mono-, di-, and trifunctional octyl and octadecyl derivatized reversed-phase high-performance liq. chromatog. silicas were exposed to very aggressive mobile phases like the medium of 6 M NaOH in MeOH/H2O (50/50 vol./vol.). 29Si NMR was used to study the dissoln. characteristics of these phases by monitoring the concns. of the dissolving silane and silica structures. Dissoln. products of alkylchlorosilanes were used as model compds. for assignment purposes. Octadecyl phases appeared to degrade by dissoln. of the silica substrate; octadecylsilane structures were insol. under the exptl. conditions. Monofunctional octyl phases were shown to deteriorate through initial dissoln. of monomeric ligand silane particles, wheres for difunctional octyl phases, the silica backbone appeared to dissolve with the silane ligands still attached. The latter mechanism was also obsd. for the trifunctional octyl phases, but these phases resemble octadecyl phases, probably because the free ligand silane particles are almost insol. and the major cause of phase degrdn. is dissoln. of the silica substrat

Patching in reversed-phase high-performance liquid chromatographic materials studied by solid-state NMR spectrometry

The distribution of silane chains over the silica gel surface in reversed-phase high-performance liq. chromatog. (RP-HPLC) phases was studied with special attention being paid to surface homogeneity: there might be areas with high coverage and areas with low coverage of silane chains, hence clustering or patching of the silane chains can occur. Two RP phases were studied before and after well conditioned aging, together with 4 silylated silica gels (serving as models). Two solid-state NMR techniques (e.g.,1H-29Si dipolar dephasing 29Si cross-polarization magic angle spinning NMR and 13C spin-lattice relaxation in the rotating frame) were used. For the 4 model compds. with varying degrees of coverage, only differences in the NMR time consts. were obsd. between the maximally covered phase and the 3 less densely covered silica gels. This proves that silane chains on an RP phase with max. coverage are restricted in their mobilities with respect to the less densely packed materials. For the 2 non-aged RP phases, the silane chains are probably homogeneously distributed over the silica gel surface. Further, the non-aged RP phases were compared with their counterparts, aged under well defined exptl. conditions. After aging, no differences were found between the original and the aged phases, now indicating however, that patching had developed upon agein