Synthesis and adsorption properties of restricted access sorbents based on hypercrosslinked polystyrene

Abstract

Currently solid-phase extraction (SPE) is actively employed to analyze medicinal compounds both
in waste waters and physiological liquids, mostly plasma and serum. Industrial hypercrosslinked polystyrene
sorbents used in the analyses, in most cases have a wide particle size distribution of 40 to 14 µ. They provide
high recoveries of medicines thereby increasing the accuracy of analyses. However, the modern tendency to
decrease analyses time and miniaturize embodiment requires the application of sorbents with spherical beads
of 30-60 µ and sufficiently narrow bead size distribution. It proved to be possible to prepare such beads by
suspension copolymerization of styrene and divinylbenzene on the implementation of some specific conditions.
First of all, it should be noted that not only an intensive agitation of reaction mixture, but also the type
of the stirrer (we use a centrifugal one), the form of vessel and the ratio of their sizes are very important. To
avoid the formation of particulate, it is necessary to minimize the volume of a free space over the reaction
mixture and realize its appropriate heating. It is also important to eliminate any vibration of equipment. Taking
into account all aforementioned requirements and using the speed if stirrer of 1750 rpm, we prepared
styrene-0.7% divinylbenzene copolymer with desirable type of beads. Then, the copolymer was crosslinked
with monochlorodimethyl ether to 100 and 200% crosslinking density via Friedel-Crafts reaction. The resulting
sorbets possessed high specific inner surface of 1200 and 1500 m2
/g, respectively. Under static conditions,
0.125 g sorbent extracts 83 to 95% phenylcarboxylic acids (markers of sepsis) from 10 mL aqueous 10-
4
M solution acidified to pH 4. The sorbent with 100% bridges absorbs 95% of globular protein Cytochrome
C from 0.88 g/L solution in phosphate buffer with pH 6.86. However, the increase in crosslinking degree till
200% diminishes the adsorption capacity down to 25%. Importantly, both sorbents do not take up the major
blood protein, albumin. This fact allows the assignment of hypercrosslinked sorbents to the family of re-stricted accuses materials. However, contrary to well-known materials based on silica gels, the hypercrosslinked
polystyrene is more universal and its synthesis is simper. Direct chromatographic experiment showed
that under HPLC conditions, the column packed with a hypercrosslinked polystyrene sorbent is capable of
separating into the individual components the mixture of plasma, the drug Amperozide, its metabolite and
related compounds, at that plasma is not retained by the sorbent; it leaves the column with a void volume.