Sample cleanup size-exclusion

For multi-analyte and/or multi-matrix methods, it is not possible to validate a method for all combinations of analyte, concentration and type of sample matrix that may be encountered in subsequent use of the method. On the other hand, the standards EN1528 andEN 12393 consist of a range of old multi-residue methods. The working principles of these methods are accepted not only in Europe, but all over the world. Most often these methods are based on extractions with acetone, acetonitrile, ethyl acetate or n-hexane. Subsequent cleanup steps are based on solvent partition steps and size exclusion or adsorption chromatography on Florisil, silica gel or alumina. Each solvent and each cleanup step has been successfully applied to hundreds of pesticides and tested in countless method validation studies. The selectivity and sensitivity of GC combined with electron capture, nitrogen-phosphorus, flame photometric or mass spectrometric detectors for a large number of pesticides are acceptable. 

Two approaches are generally used to develop methods with lower detection and quantitation limits for target compounds. One approach involves the use of sample cleanup methods such as size exclusion chromatography (SEC) for the... 

EROD activity is measured in the H411E cells as follows. The cells are seeded at 7,000 cells per well in 250 xL of Dulbecco s modified Eagles culture media (Tillitt et al., 1991). After an initial incubation period of 24 hours, the cells are dosed with 5 xL volumes of eiuiched SPMD extracts (cleanup of extracts generally includes dialysis and size exclusion chromatography [SEC]) and incubated for an additional 72 hours. Sample dose is typically expressed as g-equivalents triolein or whole SPMD per mg cellular protein. Multiple exposures are performed at each of six (typically) sample concentrations, using a dilution series. Afterwards, the microtiter plates are washed three times with distilled water to lyse the cells. EROD activity (pmol mg cellular protein per min) in each sample is measured... 

Most environmental GC analyses involve a sample cleanup procedure. For example, Schomberg (11) recommends optimized sample cleanup by using liquid chromatography with size exclusion, ion... 

Bean et al. (10) used size-exclusion chromatography to remove materials of MW >800. This method of cleanup was rejected because size-exclusion chromatography might introduce new artifacts and cause additional delays in sample analysis time. Because the matrix problem appeared to have acidic components, it was decided that a base extraction procedure might remove these materials. 

Gel permeation chromatography (GPC), also called size-exclusion chromatography, is the most widely used cleanup technique for pesticides in fatty foods. It is the method of choice for rapid cleanup of biological extracts, especially from high-fat samples, to determine pesticide residues, since separation occurs on the basis of molecular size (7). 

Today, there is strong interest in the development of online sample treatment techniques that allow the handling of untreated biological samples. Thus, in online SPE-LC, deproteination of plasma and serum is required before extraction, especially if the same cartridge is used for repeated analysis. For this purpose, restricted-access materials (RAMs) have been developed, which combine size-exclusion and reversed phase mechanisms, allowing extraction and cleanup of samples in the same step. RAMs have became quite popular for the direct injection of biological fluids, since they prevent the access of matrix components (e.g., proteins) while retaining the analytes in the interior of the sorbent. 

With the exception of mold culture extracts, which can be analyzed directly after extraction, the mycotoxin from a test sample must be concentrated and purified. Various techniques, such as column chromatography on silica gel, octadecyl-bonded silica gel, alumina, magnesium silicate, size-exclusion gels, charcoal, ion-exchange bonded phases, or immunoaffinity packing, are used. The most commonly used column packing is silica gel. Lipid material is eluted first with a nonpolar solvent such as hexane. The mycotoxin of interest is eluted with a solvent that will remove all of the mycotoxin but leave other material on the column. Solvent partition, metal complexation, ion-pairing, and precipitation are also used for purification. Smaller cleanup columns, which use less solvent, have... 

The use of liquid chromatography for the analysis of chlorinated aromatic compounds is rarely reported. An exception exists for LC methods used for sample cleanup. The complexity of environmental samples often necessitates the fractionation of sample extracts, which are then analyzed separately by GC-based methods. These LC fractionation methods have been developed based on size-exclusion chromatography... 

Microdialysis can achieve both sample recovery and cleanup before analysis. The pore size of the microdialysis membrane can be tailored for selective exclusion of macromolecules such as proteins and enzymes, thus producing cleaner samples with reduced possibility of enzymatic degradation of the sample. 

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