Additivity of retention of diastereoisomeric and enantiomeric arylphthalides, aryl(arylene)phthalides and aryldiphthalides of dyadic and triadic composition.

For the first time, four series of new phthalide-containing heteroaromatic compounds were separated by reverse phase HPLC: OYO, OYS, SYS; OYOYO, OYOYS, SYOYS; SYSYS, SYSYO, OYSYO; OYYO, OYYS, SYYS, (where O - diphenyloxide, S - diphenylsulfide, Y - phthalide group). A fundamental difference was established in the chromatographic behavior of diaryl(arylene)diphthalides, built on the principle of "head-to-tail", and diaryldiphthalides with a structure of "head-to-head". The meso and chiral diastereoisomers of the former were eluted by one peak, while the latter existed in solution in the forms of stable cis (racemic form) and trans (meso form) rotamers with different retention times. It was shown that to calculate the retention times of related diarylphthalides, diaryl(arylene)phthalides, diastereoisomeric and enantiomeric diaryldiphthalides of an asymmetric structure, the half-sum rule can be applied according to which: tR(A-X-B)≈[(tR(A-X-A)+tR(B-X-B)]/2. For diaryl(arylene)diphthalides of a triadic structure, a modified additive scheme for calculating retention times is proposed, including multiplication and division operations: tR(A-A-A) = tR(A-A-B) × tR(A-B-B)/tR(B-B-B).

Elucidation of retention mechanisms on hypercrosslinked polystyrene used as column packing material for high-performance liquid chromatography.

Establishing of basic retention mechanisms was considered the key target during the development of new column packing materials. To extract, from an appropriate retention data matrix on hypercrosslinked polystyrene Chromalite 5HGN, certain factors that can be brought in an obvious correspondence with known retention mechanisms, the principal component analysis (PCA) was applied. The approach was used to elucidate the adsorption properties of the above novel HPLC packing. Besides HPLC, knowledge of retention mechanisms helps to reveal perspective application area for the hypercrosslinked polystyrene-type materials in solid-phase extraction (SPE) and low-pressure preparative LC.

Hypercrosslinked polystyrene as a novel type of high-performance liquid chromatography column packing material. Mechanisms of retention.

An experimental material, Chromalite 5HGN (Purolite, UK), that represents hypercrosslinked polystyrene as a new type of neutral stationary phase for HPLC was examined. The material contains no functional groups, but is compatible with any kind of nonpolar and highly polar mobile phase, and even with water. It is chemically resistant and thermally stable. When using aqueous organic mobile phases, Chromalite 5HGN works similar to standard C18 reversed-phase packings, but is characterized by much greater hydrophobicity and, sometimes, unusual selectivity. When using nonpolar mobile phases, i.e. under "quasi normal-phase" conditions, the retention is mostly governed by the interactions between pi-electronic systems of the adsorbent and adsorbate. Adding highly polar, even hydrophilic solvents into the mobile phase, leads to a shift of retention times toward the "reversed-phase" kind of chromatography, which gives an additional possibility in fine tuning the column selectivity.

Mass-spectrometric analysis of N-acetylchitooligosaccharides prepared through enzymatic hydrolysis of chitosan.

A semipreparative scale chromatography of N-acetylchitooligosaccharides (GlcNac)2-7 on a reversed-phase C-16 HPLC column is reported. The initial material was obtained by enzymatic hydrolysis of chitosan with a complex of chitinases from Streptomyces kurssanovii, followed by a complete acetylation of amino groups. Isolated N-acetylchitooligosaccharides were characterized by the mass-spectrometric method. On interacting with the sample, the fragments of 252Cf caused desorption of quasi-molecular ions of the substance. All mass spectra of chitin oligomers contained intense quasi-molecular ions [M + Na]+ and a less intense [M + K]+ ion. Fragment ions, compared to the quasi-molecular ion [M + K]+, had a lower intensity and confirmed the structure of samples under study. Due to this phenomenon, an accurate analysis of both individual compounds and mixtures of N-acetylchitooligosaccharides (n = 2-7) may be performed.