Column cleanup

Add 0.5-0.75 in of anhydrous sodium sulfate to the head of a 6-mL silica disposable column to ensure removal of any residual water, and attach a 15-mL reservoir to the top of each column. Place the desired number of silica cleanup columns into the female Luer receptacles on the cover. Turn the vacuum on at the source, and set the vacuum to about 10 inHg. Wash each column with isooctane. If the column goes dry, add an additional 10 mL of isooctane. When the solvent in the column reaches the top of the packing bed, turn the flow control valve fully off. 

The variety of cleanup columns included may allow for rapid adaptation to additional matrices. If using hexane-diethyl ether (15 1, v/v) as an eluent, this solution should be prepared just prior to use. Cleanup with silica gel and hexane-ethyl acetate (4 1, v/v) is recommended for most crop samples. 

Each batch of alumina, Horisil, and silica gel used in a cleanup column must be checked for recovery of pyriproxyfen. If the recovery of pyriproxyfen is <90%, the elution volume and/or solvent mixture must be adjusted until suitable recoveries are obtained. 

This result is important to fully understanding the biochemical and ultra-structural origin of peaks and the physiological basis for variation. It not only helps in designing the analytical strategy (e.g., in selection of cleanup columns) but, more important, in making a decision on whether the marker should be used for strain or species identification or for biodetection. For example, there are a number of low-molecular weight peptides (1500-8000 kDa) present in... 

A cleanup column from a commercial source can be used or can be constructed easily from a Pasteur pipette (see Figure 12.12). A small piece of cotton is placed in the bottom of the pipette. A suitable absorbant, such as a solid coated with or bonded to a high-molecular-weight hydrocarbon such as octadecanol (this is often simply called a C-18 extraction column), can be loaded into the pipette and covered with another small amount of a cotton ball. A list of common extract cleanup absorbants and their characteristics is given in Table 12.3. 

Even thongh cleanup procedures are advocated before sample analysis, there can be several limitations to varions cleannp steps. The reasons for decreased effectiveness of cleanup procedures include (1) Sample loading may exceed the capacity of cleanup columns, (2) nonpetrolenm componnds may have chemical strnctnres similar to petroleum constituents and may behave like a petroleum constituent, (3) analytes of interest may be removed dnring the cleanup and (4) no single cleanup technique removes all the chemical interference. 

Figure 9—2 shows the plant with its three reactors. The pyrolysis furnace is in the middle. At the top of the figure, the basic feeds, to the plant are shown—ethylene, chlorine, and oxygen. Ethylene and chlorine alone are sufficient to make EDC via the route on the left. The operation, call it Reaction One like Figure 9-1 does, takes place in the vapor phase in a reactor with a fixed catalyst bed of ferric (iron) chloride at only 100—125°F. A cleanup column fractionates out the small amount of by-products that get formed, leaving an EDC stream of 96—98% purity. 

EPA Method No. Parameters Method Cleanup Column Temp. (°C) Detectora... 

TJ Wilson, TR Romer. Use of the Mycosep multifunctional cleanup column for liquid chromatographic determination of aflatoxins in agricultural products. J Ass Off Anal Chem 74 951-956, 1991. 

For florisil cleanup, column eluted with methylene chloride/hexane (1 9) and then with acetone/methylene chloride (1 9) mixture analyte eluted into the latter fraction. 

Compound(s)1 Source of PGS Prior sample cleanup Column Analytical identification Ref. 

Marko Varga et al. [45] found that a cleanup column prior to the separation column, packed with a chemically bonded amine material (Nucleosil 5 HN2) was found to be effective in removing interfering humic substances. No influence was found from humic substances in concentrations up to 45 pg L 1 on ion chromatographic analysis of nitrate and sulphate (10-100mg L ) after passage through the cleanup column. 

When the sample is transferred to the cleanup column, it should be dissolved in the same solvent used for elution or one of lesser polarity. The volume should be no greater than 1 ml. 

A microcolumn packed with 3 g of activated silica gel is used for sample cleanup and fractionation. An aliquot of the extract (containing about 20 mg oil or TSEM) is then transferred to the silica gel cleanup column to remove polar components and other interferences. The column is eluted first with hexane, which recovers samrated hydrocarbons as Fraction 1 (FI). The mixture of hexane/DCM or hexane/benzene (1 1, v v) is used to elute the aromatic compounds as Fraction 2 (F2). Half of FI and half of F2 are combined into the Fraction 3 (F3). These three fractions are concentrated to appropriate volume (0.5 to 1.0 ml) by nitrogen purge. The quantitation internal standards are 5-a-androstane, di4-terphyl, and C30 17(3(H), 21(3(H)-hopane. The Fraction 3 is analyzed for quantitation of the TPH and the UCM by GC-FID. The Fraction 1 is analyzed for determination of n-alkanes by GC-FID and biomarker terpanes and steranes by GC-MS. The Fraction 2 is analyzed for the determination of alkylated PAH homologues and other EPA priority unsubstantiated PAHs by GC-MS. 

Continued progress on the development of improved sample cleanup techniques with good recoveries has been observed. An example of the application of a new cleanup column was an improvement of a fluorometric test kit that determines AFL in almonds, allowing it to be validated by the AOAC International Research Institute as a Performance Tested certified kit (Romer Labs, 2007). 

Before hybridization to a microarray, the biotin-labeled RNA must be purified away from unincorporated nucleotides. It is inadvisable to perform this operation using a phenol chloroform approach because the biotin causes some of the RNA to be partitioned into the organic phase, thus lowering the yield. Instead, use the same cleanup columns used to purify the cDNA reaction (GeneChip sample cleanup module, Affymetrix). Before proceeding, ensure that buffers have been diluted with ethanol where appropriate. This protocol is supplied by the manufacturer and is described here with minor modification... 

Extraction Cleanup column Derivatization Determination Toxins analyzed Detection limit (NIV) Commodities References... 

SPE is used to concentrate solutes from dilute solution, for example collection of nonpolar organic constituents from water on C-18 columns. The compounds are recovered by elution from the column with a few ml of an appropriate solvent and spotted for TLC. The concentration factor obtained is the ratio of the sample volume to the elution volume. In some cases, the eluate must be cleaned up further prior to TLC. An example of this trace enrichment process is the determination of the pesticide diflubenzuron in water by densitometric TLC (81), SPE can also be used to purify concentrated solvent extracts, in place of classical large cleanup columns that require up to hundreds of milliliters of eluent. SPE columns are eluted usually with only several milliliters of solvent. A sequence of eluents of increasing strength can be used to elute compounds with different polarities in separate fractions, and multiple columns can be connected in series for improved cleanup and/or fractionation. 

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... 

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