Trace enrichment of phenylcarboxylic acids from a model biological fluid and serum of human blood.

The study was focused on the development of a solid-phase extraction protocol for seven phenylcarboxylic acids from albumin solutions by using unmodified hyper-cross-linked polystyrene restricted access materials with crosslinking degrees varying from 100 to 400% (four of the acids are known to be markers of sepsis). The breakthrough volume of the most hydrophilic 3,4-dihydroxybenzoic acid rises as the sorbent bridging extent grows. Inversely, the breakthrough volume of the most hydrophobic 3-phenylpropionic acid was found to decrease considerably when the degree of crosslinking exceeds 200%. This unusual pattern is because of the superposition of two opposite tendencies. Increasing substitution extent of phenyls facilitates their π-π-interactions with polar compounds whereas rising density of the network reduces the accessibility of sorption sites to all solutes. Mini-cartridges containing 30 mg of an optimal sorbent take up the acids completely and reversibly, the recoveries being close to 100% even in the presence of high concentrations of albumin. By coupling the developed solid-phase extraction with high-performance liquid chromatography and diode array detection technique, we managed to determine quantitatively phenylcarboxylic acids in the serum of a healthy patient blood, and the recoveries varied from 93 to 100% while the limit of quantification was (4-9) × 10-7  M.

Hypercrosslinked polymeric restricted access materials for analysis of biological fluids.

New restricted access materials based on microporous hypercrosslinked polystyrene have been developed. The materials are aimed to use as packings for solid-phase extraction cartridges to isolate low-molecular-weight analytes from biological fluids (for instance, blood plasma or serum). Two features distinguish these polymers from all known restricted access materials. The first one consists of the microporous hypercrosslinked polystyrene that not only exclude proteins from the sorbent phase but also do not adsorb them on the bead outer surface, and so they do not cause coagulation of blood protein components. Therefore, these materials do not require any chemical modification. The second distinguishing feature is the ability of hypercrosslinked sorbents to take up a wide variety of polar and nonpolar organic compounds. The sorbents were obtained in the form of beads of 60-70 µm in diameter by cross-linking styrene copolymers with 1, 2, and 3% divinylbenzene with monochlorodimethyl ether to 100, 150, and 200% cross-linking degree. The sorbents exhibit all typical properties of hypercrosslinked networks. They do not take up albumin, the major blood protein, and cytochrome C, representative of smaller protein molecules, but are capable of adsorbing drugs, vitamins, and phenyl carboxylic acids (markers of sepsis) from model aqueous solutions.

Physicochemical and adsorption properties of hypercross-linked polystyrene with ultimate cross-linking density.

The paper describes unexpected properties of hypercross-linked polystyrenes with ultimate cross-linking degrees of 300, 400, and 500%, where three, four, or five methylene links, respectively, could bind each polystyrene phenyl ring to its spacious neighbors. The polymers exhibit a strong electron spin resonance signal, unusual spectra in IR, UV, and visible ranges, and they are not typical dielectrics. The nonfunctionalized hypercross-linked polymers absorb significant amounts of inorganic acids, salts, and bases due to interactions of protons or other cations with electron-donating fragments of the aromatic network with the high extent of mutual connectivity and also due to dispersion interactions of anions with the polymer matrix.

Self-concentration effects in preparative SEC of mineral electrolytes using nanoporous neutral polymeric sorbents.

Separation of mineral electrolytes according to size exclusion mechanism using neutral nanoporous polystyrene sorbents and carbonaceous materials has been examined in detail on hand of HCl and CaCl2 solutions, taken separately and in the mixture. Phase distribution coefficients of the above electrolytes have been measured under static conditions at different concentrations. The k-values and their dependence on the concentration were correlated with the elution curves of the components from a chromatographic column. Both the static and dynamic data suggest a strong dependence of the hydration number and effective size of ions on the concentration. Self-concentration of HCl in small pores and that of CaCl2 outside of small pores exhibits itself in both static and chromatographic experiments and results from the relocation of the components largely within the volume of the initial mixture. Additional apparent "retention" of HCl in the porous volume of the sorbent in concentrated electrolyte mixtures was shown to be caused by the competition between all ions of the system for hydration water. Increased separation selectivity and enhanced self-concentration effects for more concentrated mixtures point to preparative and industrial perspectives of size exclusion chromatography (SEC) of complex electrolyte mixtures on nanoporous neutral sorbents.

Chromatographic resolution of a salt into its parent acid and base constituents.

Based on the results of the earlier proposed process of separation of mixtures of mineral electrolytes by size-exclusion chromatography (SEC), it has been suggested that a mineral salt must spontaneously resolve, at least partially, into its parent acid and base constituents, provided that the separating media discriminates the anion and cation of the salt according to their size. Indeed, migration of a zone of an aqueous salt solution through a bed of neutral nanoporous hypercrosslinked polystyrene-type packing was shown to result in the generation of acidic and alkaline effluent fractions. The principle of spontaneous salt resolution has been extended to other types of discriminating interactions between the stationary phase and the two ions of the salt. The idea was exemplified by the resolution of ammonium acetate, due to hydrophobic retention of the acetate, into fractions enriched in ammoniac and then acetic acid.

Preparative frontal size-exclusion chromatography of mineral ions on neutral hypercrosslinked polystyrene.

Hypercrosslinked polystyrene, being the first and the only one accessible for water microporous hydrophobic polymeric sorbent, was found to provide efficient separation of inorganic electrolytes under conditions of a frontal size-exclusion chromatography (SEC). The process, based on the difference in size of hydrated competing ions, permits separations of many pairs of salts, acids, and bases. The productivity of separation increases with the concentration of the feed solution rising. Remarkably, concentrations of the separated components in corresponding fractions may substantially exceed those in the initial mixture, which can be explained in terms of a conception of an ideal separation process.

The next step from high-flux dialysis: application of sorbent technology.

The current foci of renal replacement therapy with dialysis are middle molecular weight toxins, consisting of small proteins, polypeptides and products of glycosylation and lipoxygenation. Conventional high-flux dialysis is not efficient at removing these molecules, explaining the increased interest in using sorbents to supplement dialysis techniques. Prototype biocompatible sorbents have been developed and investigated for middle molecule removal; these have been shown, in man, to remove beta(2)-microglobulin, angiogenin, leptin, cytokines and other molecules, without reducing platelets and leukocytes. Extensive clinical studies are underway to demonstrate the clinical utility and safety of adding routinely a sorbent hemoperfusion device to hemodialysis.