Solid phase extraction preparation

Prepare the solid-phase extraction (SPE) tube (1 ml LC-18 SPE tube) by conditioning with 1 ml of methanol followed by 1 ml of water. 

It is also possible to perform preparative TLC, developing the sample with AMD technique [36a]. After a solid-phase extraction of the waste water with C18-Empore discs, alkanesulfonate is isolated by using a specially dimensioned TLC plate and by scraping out the surfactant-containing zone. 

This sample preparation involved, firstly, an extraction and the elimination of the solid matrix by filtration and, secondly, a concentration procedure employing a solid phase extraction cartridge. The compounds of interest were separated solely by dispersive interactions with the reversed phase. In the example given, the corn meal was spiked with the aflatoxins. 

Table 3 Summary of solid-phase extraction techniques applied to the preparation of water samples for the determination of triazine pesticides...

The need to understand the fate of pesticides in the environment has necessitated the development of analytical methods for the determination of residues in environmental media. Adoption of methods utilizing instrumentation such as gas chro-matography/mass spectrometry (GC/MS), liquid chromatography/mass spectrometry (LC/MS), liquid chromatography/tandem mass spectrometry (LC/MS/MS), or enzyme-linked immunosorbent assay (ELISA) has allowed the detection of minute amounts of pesticides and their degradation products in environmental samples. Sample preparation techniques such as solid-phase extraction (SPE), accelerated solvent extraction (ASE), or solid-phase microextraction (SPME) have also been important in the development of more reliable and sensitive analytical methods. 

Specific extraction methods are used to prepare the analyte for immunoassay by freeing the analyte fromboth specific and nonspecific interferences. Supercritical fluid extraction has been used to decrease the amount of solvent waste generated. Solid-phase extraction has gained popularity, and many different supports are available. One promising extraction and concentration method is immunoaffinity chromatography, which will be addressed later. 

Kennedy et al. developed a lasalocid immunoassay for application to residues in chicken meat and liver samples. The antibody was specific and did not cross-react with salinomycin, maduramicin, or monensin. Sample preparation consisted of homogenization in aqueous acetonitrile, removal of fat from an aliquot of the aqueous acetonitrile by hexane extraction, and evaporation of acetonitrile. The sample was then reconstituted with assay buffer. Liver required an additional solid phase extraction step. The LOQ was 0.02 xgkg for muscle and 0.15 agkg for liver. These workers were able to use the system to determine the half-life of lasalocid in the tissues. 

Principles and Characteristics Solid-phase extraction (SPE) is a very popular sample preparation and clean-up technique. In SPE solutes are extracted from a liquid (or gaseous) phase into a solid phase. Substances that have been extracted by the solid particles can be removed by washing with an appropriate liquid eluent. Usually, the volume of solvent needed for complete elution of the analytes is much smaller (typically < 1 mL) than the original sample volume. A concentration of the analytes is thus achieved. 

P.D. McDonald and E.S.P. Bouvier, Solid Phase Extraction Applications Guide and Bibliography, A Resource for Sample Preparation Methods Development, Waters, Milford, MA... 

M. Zief and R. Kiser, Solid Phase Extraction for Sample Preparation, J.T. Baker, Phillipsburg (1988). 

GC, utilizing flame ionization detection (FID), has been used to measure diisopropyl methylphosphonate in meat, grain, or milk (Caton et al. 1994). Sample preparation steps include homogenization, filtration, dialysis, and extraction on a solid sorbent. Two common solid phase extractants, Tenax GC and octadecylsilane bonded silica gel (C18 Silica), were compared by Caton et al. (1994). They reported 70% recovery when using Tenax GC and 85% recovery when using C18 Silica. Sensitivity was not reported. Equilibrium experiments indicate that 8-10 mg of Tenax GC are required to achieve maximum recovery of each g of diisopropyl methylphosphonate (Caton et al. 1994). By extrapolating these... 

Kobylinska et al. [62] described a high performance liquid chromatographic analytical method for the determination of miconazole in human plasma using solid-phase extraction. The method uses a solid-phase extraction as the sample preparation step. The assay procedure is sensitive enough to measure concentrations of miconazole for 8 h in a pharmacokinetic study of Mikonazol tablets and Daktarin tablets in human volunteers. The pharmacokinetics of the two formulations was equivalent. 

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