Normal phase Florisil

Liquid chromatographic cleanup has traditionally been used with normal phase (Florisil, alumina, silica) or reversed-phase (Cig) columns. In most cases, the aim is to remove the bulk of... 

Liquid chromatographic clean up [441,443,450] has been used either in normal phase flow using alumina, silica, or florisil [22,189,403,481,484] or with reverse-phase (RP) columns [409,452,480]. In most cases these techniques are well established and are used in an off-line mode, primarily to remove the bulk of co-extracted materials prior to a more refined clean-up prior to the final determination. These columns may be prepared in the laboratory [22,403 -405] or commercial solid phase extraction (SPE) cartridges can be used [409,452, 463,470,485,486]. In both cases, the normal phase cartridges and column materials are disposable since many of the polar co-extractants bind firmly to the substrate surface and are difficult to remove. This has been overcome to some... 

Normal-phase adsorption on silica gel with a relatively less polar mobile phase is the most widely used mode in conventional TLC. To improve separations, silica gel may be impregnated with various solvents, buffers, and selective reagents. Other commercial precoated layers include alumina, florisil, polyamide, cellulose, and ion exchangers. 

Chromatographic Mode Normal Phase (Silica, Florisil , Alumina, Diol, NH2, etc.) Reverse Phase (C18, CN, etc.) Ion Exchange (NH2, Anion Exchange, Cation Exchange, etc.)... 

Normal-phase sorbents such as silica and Florisil are used to isolate low to moderate polarity species from nonaqueous solutions. Examples of applications include lipid classification, plant pigment separations, and separations of fat-soluble vitamins from lipid extracts, as well as the clean-up of organic solvent concentrates obtained from a previous SPE method or liquid-liquid extraction. Alumina is used to remove polar species from nonaqueous solutions. Examples include vitamins in feeds and food and antibiotics and other additives from feed. Normal-phase chromatography has been used for a number of years, and most applications for normal-phase column chromatography may be easily transferred over to normal-phase SPE. 

As early as the 1930s, silica, alumina, Florisil, and kieselguhr (diatomaceous earth) were used as solid sorbents for normal-phase sample concentration, for what would now be called normal-phase SPE. The next major development occurred in 1941 when Martin and Synge (Nobel Prize for work in chromatography) published their work on partition chromatography. They... 

The types of nonbonded phases used for normal-phase SPE are silica, alumina, and magnesium silicate (Florisil). The most popular phase is silica. Several bonded phases may also be used for normal-phase SPE, including aminopropyl, cyanopropyl, and propyldiol (Table 1.1, Fig. 2.7). Water is not used in the mobile phase in normal-phase SPE because it will sorb to the active sites of the sorbent and reduce the interaction between analyte and sorbent. Typically, normal-phase SPE is used as a clean-up procedure for organic extracts of water, soil, food, or other materials. Normal-phase SPE is also used for the isolation of analytes from organic liquids, such as oils. 

Alumina may also be used as a sorbent in normal-phase SPE. It may be acidic, neutral, or basic depending on the pH of the wash solution used on the alumina. It too may bind solutes by hydrogen bonding, weak ion exchange, and other polar reactions. The type of alumina generally used will depend on the analytes, with basic solutes sorbed to acidic alumina and acidic analytes sorbed to basic alumina. The magnesium silicate, Florisil, may also be used in a similar fashion to silica. 

The extraction solvent should be chosen such that the analyte is extracted with as little co-extraction of interfering substances as possible. Furthermore, choose a solvent that is compatible with the solid-phase extraction method that is being used. For example, samples that are high in fat are best homogenized with nonpolar solvents, such as hexane. The use of hexane as an extractant dictates normal-phase sorbents with silica, alumina, Florisil, or a CN sorbent. Samples with high water content are best homogenized with acids, bases, or polar solvents, such as methanol, acetonitrile, or acetone. The use of methanol or one of the water-miscible solvents suggests the use of reversed phase (C-18) and dilution of the extract with water or buffer. Thus, the choice of the extraction solvent will dictate the type of sorbent that will be used in SPE. 

Normal-phase solid-phase extraction refers to the mechanism by which the analyte is adsorbed onto the polar surface of sorbent from a nonpolar solvent. The mechanism of interaction between the analyte and sorbent is a polar interaction, such as hydrogen bonding, dipole-dipole interaction, n-K interaction, and induced dipole-dipole interaction. The sorbents widely used in normal-phase SPE are silica, alumina, and magnesium silicate (Florisil), and the siUca chemically modified with polar groups like amino, cyano, or dioLThe samples for normal-phase SPE are typically dissolved in hexane or isooctane. Step elution with solvents of increasing polarity allows the separation into fractions on the basis of difference in polarity. 

Polar, normal phases (e.g., cyano, amino, diol, silica gel, florisil, alumina)... 

Normal phase materials, including unmodified silica gel, aluminum oxide, and Florisil.. separate sample constituents into fractions of comparable polarity. They are often utilized to separate and concentrate pesticides [209]-[211], PCBs [147], [209], and PCDD/PCDFs [212]-[216] from such... 

Other examples of adsorbents are alumina (acidic, neutral, and basic), magnesium oxide, magnesium silicate (Florisil), cellulose (polymer of o-glucopyranose units), and polyamide (polymer of [NH—(CH2)e—NH—CO—(CH2) —C] ). These adsorbents are, as with silica, mainly used for normal-phase TLC, while the use of cellulose is better described by a partitioning mechanism. 

Typical sorbents for normal-phase SPE are silica, cyano, did, NHz (all silica based), alumina (AI2O3 based), and Florisil (MgSi03 based) (Table 9.3). 

Normal-phase chromatography can also be applied to concentrate polar analytes that are dissolved in a nonpolar solvent, such as hexane. The hexane can be passed through a polar solid phase such as silica, Florisil, alumina, or a diol to adsorb the polar analyte. The polar analyte can be eluted with a smaller volume of a more polar solvent (e.g., ethyl acetate). Normal-phase SPE is not used very much for trace enrichment in environmental analysis, but is useful for matrix isolation and cleanup techniques. 

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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