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.