IDENTIFICATION OF THE PROCEDURAL STEPS THAT AFFECT RECOVERY OF SEMIVOLATILE COMPOUNDS BY SOLID-PHASE EXTRACTION USING CARTRIDGE AND PARTICLE-LOADED MEMBRANE (DISK) DEVICES

The experimental conditions are optimized for the recovery of a test mixture of neutral semi-volatile analytes on a cartridge and particle-loaded membrane (disk) device used for solid-phase extraction. The experimental variables investigated include: (1) selection of the type and volume of eluting solvent; (2) drying time between sample processing and elution of analytes; (3) the need for a preconditioning step prior to sample processing; (4) the need for an eluent permeation period prior to elution; (5) the use of organic solvents, surfactants and neutral inorganic salts as sample processing aids to enhance sample flow rates and recovery; (6) sample flow rate. The disk device is easier to work with, allows faster sample processing, requires a smaller eluent volume for analyte recovery, and provides recoveries virtually independent of the sample and eluent flow rates. On the other hand, preconditioning of the disk with an organic solvent prior to sample application is absolutely essential for normal operation, but is not essential when the cartridge device is used. There is greater variability in results obtained on different cartridge devices because of differences in their packing density and heterogeneous flow characteristics. The recovery of analytes from the cartridge device shows significant flow rate dependence when the sample volume exceeds the breakthrough volume of the analyte. When used under optimized conditions both devices show excellent recovery of the analytes (> 90%, except for dodecane on the cartridge device) and similar method precision.