Methods gel-permeation chromatography

Fenpyroximate and M-1 residues in the plant (apple, grape, etc.) and soil samples can be analyzed using the multi-residue method Method DFG 819 with some minor deviations. In this method, gel permeation chromatography (GPC) is effectively used as the cleanup procedure. Residues in the water sample can be analyzed by a simpler method. 

As with most other chromatographic separation methods, gel permeation chromatography-size-exclusion chromatography (GPC-SEC) is based on partitioning of analyte polymer molecules between the stationary phase (which, in the case of GPC-SEC, is contained within the pores of a porous stationary-phase support) and the mobile phase. Ideally, the mobile phase establishes a concentration equilibrium with the stationary phase at each plate in the column before being transferred to the next plate. The concentration equihb-rium is dictated by an equal chemical potential of the polymer chain between the two phases [1,2]. In normal conditions of GPC-SEC, the polymer concentration Cm in the mobile phase is sufficiently low, and the solution behaves ideally dilute. Its chemical potential per molecule in the mobile phase is then given as... 

FRACTIONATION METHODS Gel permeation chromatography emplo5ring THF as a solvent. 

Size and size distribution Dynamic light scattering method Gel Permeation Chromatography Size Exclusion Chromatography... 

Determinarion of MW and MWD by SEC using commercial narrow molecular weight distribution polystyrene as calibration standards is an ASTM-D5296 standard method for polystyrene (11). However, no data on precision are included in the 1997 edition of the ASTM method. In the ASTM-D3536 method for gel-permeation chromatography from seven replicates, the M of a polystyrene is 263,000 30,000 (11.4%) for a single determination within the 95% confidence level (12). A relative standard deviation of 3.9% was reported for a cooperative determination of of polystyrene by SEC (7). In another cooperative study, a 11.3% relative standard deviation in M, of polystyrene by GPC was reported (13). 

ASTM D-3536-91, Standard Test Method for Molecular Weight Averages and Molecular Weight Distribution by Liquid Exclusion Chromatography (Gel Permeation Chromatography-GPC), ASTM Annual Books of ASTM Standards, Vol. 08.02, P. 349—359. This method was deleted in the 1997 edition of the ASTM book. 

Nonionic surfactants, including EO-PO block copolymers, may be readily separated from anionic surfactants by a simple batch ion exchange method [21] analytical separation of EO-PO copolymers from other nonionic surfactants is possible by thin-layer chromatography (TLC) [22,23] and paper chromatography [24], and EO-PO copolymers may themselves be separated into narrow molecular weight fractions on a preparative scale by gel permeation chromatography (GPC) [25]. 

Gel permeation chromatography (GPC) or size exclusion chromatography (SEC) has been routinely used to estimate die molecular weight of die polymers. The molecular weight measured by GPC is relative to a polymer standard, typically polystyrene GPC is dius a relative method rather than an absolute one. For those polymers whose structure is very different from polystyrene, GPC molecular weight values could significantly differ from the real ones. In those cases, GPC values should only be regarded as a reference. 

Analysis of Data. Gel Permeation Chromatography (GPC) was used to determine the molecular weights and molecular weight distribution of the seed and polymers that were produced. A modified version of Smith s (31) method was used to convert the GPC data to molecular weights and molecular weight distribution. 

In principle all methods except viscosity measurement can be used to obtain absolute values of molar mass. Viscosity methods, by contrast, do not give absolute values, but rely on prior calibration using standards of known molar mass. The relationship between polymer solution viscosity and molar mass is merely empirical but the techniques are widely used because of their simplicity. All of the absolute methods are time-consuming and laborious and are not used on a routine basis. As well as the techniques already mentioned, there is the size-exclusion method of chromatography known as Gel-Permeation Chromatography (GPC). All of these methods are discussed in detail in the sections that follow. 

Gel permeation chromatography (GPC) is a widely used technique for determining molar mass and molar mass distrihution of polymers. In its usual form it is not an absolute method, though hy making the appropriate measurements it may be made to be so. 

The method of choice for the determination of a- and P-endosulfan in blood, urine, liver, kidney, brain, and adipose tissue is gas chromatography equipped with an electron capture detector (GC/ECD) (Coutselinis et al. 1976 Demeter and Heyndrickx 1979 Demeter et al. 1977 Le Bel and Williams 1986). This is because GC/ECD is relatively inexpensive, simple to operate, and offers a high sensitivity for halogens (Griffith and Blanke 1974). After fractionation of adipose tissue extracts using gel permeation chromatography, detection limits of low-ppb (1.2 ng/g) were achieved for endosulfan and other chlorinated pesticides using GC/ECD (Le Bel and Williams 1986). 

A reliable chromatographic method has been developed for the quantitative aneilysis of hydrophobic impurities in water-soluble polymeric dyes. The method utilizes both the molecular sieve effect of normal gel permeation chromatography and solute-column packing interaction, modified by solvent composition. This method eliminates the need to extract the impurities from the polymeric dye with 100 extraction efficiency, as would be required for an ordinary liquid chromatographic analysis. 

The Guidance Document on Residue Analytical Methods requests the applicant to assess a standard multi-residue method by using standard steps. These steps are extraction with acetone or ethyl acetate, cleanup by gel permeation chromatography (GPC) and/or silica gel chromatography and final determination by GC. 

In both cases, the entire method consists of four stages solvent extraction and partition, cleanup by gel permeation chromatography (GPC) and/or mini silica gel column chromatography and gas chromatography (GC) determination. Except for the central GPC, several variations occur at each stage depending on the kind of sample material and the residues to be analyzed. The variations can be combined with each other in a variety of ways according to the requirements. 

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