DETERMINATION OF KINETIC AND RETENTION PROPERTIES OF CARTRIDGE AND DISK DEVICES FOR SOLID-PHASE EXTRACTION

The kinetic properties of cartridge and disk solid-phase extraction de vices are determined by forced-flow liquid chromatography. Typical car tridges provide about 5-15 theoretical plates per cm of bed height and particle-loaded membranes provide about 4-9 theoretical plates for a 0.5-mm-thick membrane. It is shown that cartridge devices fail to prov ide their maximum trapping performance because of inadequate packing d ensity and that the required packing density could be easily achieved in practice with particles of a standard size. The retention propertie s of common sorbents for extraction from water and air are characteriz ed with the solvation parameter model. For predominantly aqueous solut ions a favorable cavity term results in increased retention while pola r interactions tend to reduce retention. Retention on porous polymer s orbents is more complicated because of their capacity to absorb signif icant amounts of the sample processing solvent resulting in solvent-de pendent changes in retention properties. For trapping organic volatile s from air cavity formation and dispersion interactions are important, and in the case of Tenax its capacity for induction interactions is a lso significant.