Chemically modified polymeric resins for separation of cations, organic acids, and small polar molecules by high performance liquid chromatography

• Main Author: Morris, John Brennan
• Format: Text
• Language: English
• Published: Iowa State University Digital Repository 1993
• Subjects: Chemistry; Analytic; Analytical Chemistry; Polymer Chemistry; Carbonic acid
• Online Access: https://lib.dr.iastate.edu/rtd/10254; https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=11253&context=rtd

Simple organic reactions are used to chemically modify macroporous polystyrene-divinylbenzene resins. Cation separations are studied on weak-acid resins that are easily synthesized and carry the exchange group on the free aromatic portion of the repeating styrene unit of the resin or on a short spacer arm from the ring. The synthesis and general properties of two carboxylic acid resins are described. A higher exchange capacity is required for effective ion chromatographic separations than that needed for sulfonated resins. A number of excellent separations are reported using eluents containing ethylenediammonium cations plus a weak complexing agent. The effect of pH on retention times of metal ions is reported;Separation of carboxylic acids and other polar compounds by ion-exclusion chromatography is usually performed on a gel-type resin column of high cation exchange capacity (either sulfonated or carboxylated). It is now shown that excellent separations can be obtained on smaller columns packed with lightly sulfonated macroporous resins. The mechanism appears to be a partitioning between the predominantly aqueous eluent and the resin matrix. Good separations were also obtained on a low-capacity macroporous resin containing a carboxylic acid functional group. Aqueous-acetonitrile eluent gradients can be used to obtain fast separation of at least 11 different carboxylic acids in a single run;Small straight-chain alcohols added to an aqueous mobile phase were found to have a dramatic effect on the chromatographic behavior of alkane carboxylic acids. The alcohols were believed to coat the resin surface and establish a dynamic equilibrium between the mobile and stationary phases. This altered the hydrophilicity of the resin surface permitting a fine-tuning of the stationary phase capacity behavior. The eluent systems have a very low background conductance, thus allowing very sensitive conductometric detection. The presence of carbonic acid (from atmospheric carbon dioxide) in the eluent was determined to play a role in the retention mechanism of the weak-acid species. The use of larger straight-chain alcohols as modifiers in a water/acetonitrile mobile phase was investigated for the separation of neutral organic species. Finally, a 12-carbon alcohol was semi-permanently coated on the PS-DVB resin. This treated column was used for separation of alkane carboxylic acids using a purely aqueous eluent and conductometric detection.