Pesticides Florisil cleanup

Sulfur is found in many industrial wastes, marine algae, and sediment samples. Sulfur may mask the region of chromatogram, overlapping with peaks of interest. For example, in pesticides analysis, sulfur can mask over many pesticides such as lindane, aldrin, and heptachlor. Sulfur has a solubility similar to the organochlorine and organophosphorus pesticides and it cannot be separated by Florisil cleanup method. 

The Florisil cleanup of pesticides is an example of classical cleanup technique that has been used extensively for years. Prior to cleanup, the sample extract should be concentrated to 10 mL and be in hexane. A column containing 20 g of Florisil with a 2-cm layer of anhydrous sodium sulfate on top of the column is... 

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. 

Prior to the development of modern SPE formats, liquid-solid partitioning with charcoal, silica, Florisil, and/or alumina was common to aid in the removal of lipids in the determination of nonpolar pesticides, but these sorbents are less useful in the cleanup of semi-polar and polar pesticides owing to the large elution volumes needed. Applications of modern SPE are discussed in Section 3.2. 

The development of solid-phase extraction (SPE) absorbents such as silica gel, alumina and Florisil tremendously aided in the purification or cleanup of pesticide residues from water. 

The basic technique of removing undesired components from a solution with the help of solids has been used for sample cleanup for a long time. The recoveries from a quick cleanup for waste solvents based on a sample filtration through a Florisil and sodium sulfate column are given in Table 2.3. It can be seen from the data in this table that a large number of pesticides are retained by Florisil. These can be recovered for appropriate analysis. 

Phthalate Esters (Method 606). These compounds are extracted with methylene chloride, concentrated, and solvent exchanged to hexane for Florisil or aluminum oxide column cleanup and EC-GC determination by using a mixed phase columnn of 1.5 SP-2250 and 1.95 SP-2401. This method is essentially the same as that for or-ganochlorine pesticides. 

Elution Patterns for Pesticides in Florisil Column Cleanup Table 2.20.3... 

The solvent extract should be subjected to one or more cleanup steps for the removal of interfering substances. The presence of phthalate esters, sulfur, or other chlorinated compounds can mask pesticide peaks. The extract should, therefore, be cleaned up from the interfering substances using a florisil column or by gel permeation chromatography (see Chapter 1.5). The distribution patterns for the pesticides in the florisil column fractions are presented in Table 2.20.2. 

Florisil column A glass column with an adsorbent that is used for sample cleanup of chlorinated pesticides and PCBs. 

Column chromatography has been widely used for the cleanup of samples, either individually or after preliminary purification by solvent partitioning. An example of the latter is the quantitative TLC determination of the fungicides captan, folpet, and captafol in lettuce and apples (79). Samples were extracted by blending with acetone and the extracts were filtered, pesticides were partitioned from the aqueous filtrate with petroleum ether-methylene chloride (1 1), the organic layer was concentrated and diluted with acetone and petroleum ether, and the solution was chromatographed on an activated Florisil column with elution by 200 ml of 15% ethyl ether in petroleum ether followed by 200 ml of 50% ethyl ether in petroleum ether. The eluates were concentrated and aliquots spotted for TLC analysis. 

For the column cleanup of pesticide-containing extracts, alumina (13), florisil (10,21), silica gel (6), and charcoal-magnesium oxide-celite mixed support (6) have been applied, and these colunms are eluted with different organic solvents or solvent systems (Table 1), changing their elution strength... 

Major matrix components or other trace organic compoimds, such as polycyclic aromatic hydrocarbons (PAH) and pesticides, are coextracted with PCBs and might cause interference to the instrumental response, thus they should be eliminated by suitable cleanup procedures. The cleanup is generally performed by column chromatography on suitably activated or deactivate silica [24,54,68,97,128,138,146], sulfuric acid impregned silica [131], alumina [9,14,15,90-92,142], or Florisil (synthetic magnesium silicate) [24,44,67,83], and styrene-divinylbenzene resin [121]. Multilayer columns are frequently utilized. The retention of analytes in the column should be checked by standard solutions in order to find both the best solvent or mixture of solvents and the optimum volume to be used to selectively elute PCBs and leave interferents in the column. n-Hexane and dichloromethane are the most widely used solvents to elute the PCBs from the stationary phase. In addition, special treatments are very often used to eliminate specific interfering substances. For instance, activated copper powder with [23] or without mercury [14,49,81,87,151] or tetrabutyl ammonium sulfite [4] is used to remove elemental sulfur and sulfuric acid is used to remove lipids [107]. 

Normal-phase liquid chromatography can be used to separate interfering compounds from SVOCs, pesticides, and PCBs. Three classical adsorbents—Florisil, alumina, and silicagel—are commonly used, although many other polar adsorbents are available. Table 15.7 shows some of the properties and characteristics of these adsorbents. Prior to the cleanup, the sample extract must be exchanged to a solvent that is compatible with the chromatographic separation. Because they are nonpolar, hexane and methylene chloride are common choices. 

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