Jacek Jagodzinski

A new approach to dealing with high-to-low concentration ratios of sodium and ammonium ions in ion chromatography

Abstract In ion chromatography, samples of very dissimilar concentration ratios of ammonium-to-sodium are difficult to quantify since these two cations have similar selectivities for stationary phases containing commonly used sulfonic acid or carboxylic acid cation-exchange functional groups. A new column with carboxylic acid and phosphonate functional groups as well as a crown ether group has been developed to address this limitation. Selectivity of the common inorganic cations is different from conventional columns in that the separation between sodium and ammonium has been greatly increased, and potassium ion elutes after magnesium and calcium. Applications involving very dissimilar concentration ratios of cations can now be done isocratically, with a single column. Other applications of this new column will also be discussed.

Anion chromatography with a crown ether-based stationary phase and an organic modifier in the eluent

Abstract The unique ability of macrocyclic ligands, such as the crown ethers and cryptands, to selectively complex alkali metal cations can be used as the basis for chromatographic separations of anions. Specifically, macrocycles which are adsorbed onto a reversed-phase column, form positively charged anion-exchange sites when they combine with eluent cations. Previously we have demonstrated gradient anion separations based on changing the column capacity during the course of the separation by altering the eluent cation, temperature, or organic modifier content using cryptand-based columns. Herein we report that excellent separations can also be achieved using 18-crown-6 based columns. In this column, anion retention increases with increasing eluent strength and organic modifier content. This observation is in keeping with the relatively moderate affinity of crown ethers for alkali metals when compared to cryptands. The separation of anions achieved by optimizing mobile phase variables shows that isocratic separations of anions on the crown-based column are almost as good as separations achieved only under gradient conditions on cryptand-based columns. Cation gradients provide additional improvements on the separations using the crown-based column.

Structure-Chiroptical Properties Relationship in Oxabicyclic β-Lactam Derivatives

The relationship between molecular structure of 5-dethia-5-oxacephams and clavams and their chiroptical properties was investigated by means of X-ray diffraction analysis, molecular modeling calculations and circular dichroism spectroscopy. It was found that the amide chromophore of the beta-lactam unit in these compounds is nonplanar with nitrogen atom having a pyramidal configuration. It was also found that the helicity of the lactam moiety in investigated oxacephams and clavams is controlled by the absolute configuration at the C-6 and C-5 carbon atom, respectively. Thus, the applicability of helicity rule correlating a positive (negative) torsional angle of the beta-lactam subunit O=C-N-C with a negative (positive) sign of the n-->pi* CE, previously applied to oxacephams, is now extended to clavams.

Chromatography on poly-RP and its cyano and diol derivatives using both polar and non-polar solvent systems

Abstract A 4-μm polystyrene-divinylbenzene resin, Poly-RP CO, was synthesized for high-performance liquid chromatography. The surface of this resin was functionalized with cyano and diol groups that are capable of enhancing the selectivity and capacity of the base resin. Chromatography was performed with traditional polar solvent systems, such as acetonitrile-water, and also with non-polar solvent systems, such as dichloromethane-hexane; the latter solvent system can give separations that are otherwise difficult to achieve with acetonitrile-water. Good separations of simple isomer mixtures were achieved on these resins.