Stationary phases solid phase extraction

Reversed-phase solid-phase extraction (SPE) involves the partitioning of organic solutes from a polar mobile phase, such as water, into a nonpolar solid phase, such as the C-18 sorbent (Fig. 4.1). Partitioning involves the interaction of the solute within the chains of the stationary phase, which may be a C-18 hydrocarbon, C-8 hydrocarbon, or the polymeric sorbents (such as styrene-divinylbenzene). The word hydrophobic mechanism is commonly... 

Polyclonal antibody Pu e-and-trap Quiescent solution Radioimmimoassay Relative affinity Reversed phase Solid-phase extraction Solid-phase microextraction Solubility Solvent extraction Solvent strength Stationary phase Thin-layer chromatography Titer... 

Five synthetic and five natural colorants were identified and quantified in lyo-philized dairy products and fatty foods using an automatic method based on solid phase extraction using a stationary phase followed by RP-HPLC C,g columns for the sequential retention of colorants and diode array detection. Lyophilization of the samples coupled with the separation procedure provided clean extracts despite the complexity of the food matrices and preserved the sample for at least 2 months without changes in colorant concentrations. The detection limits achieved for the colorants were found in a wide range from 0.03 to 75 pg/g of the lyophilized sample, according to the limits established by the European Union. ... 

Ion-exchange solid-phase extractions are used for ionic compounds. The pH of the extracts is adjusted to ionize the target analytes so that they are preferentially retained by the stationary bonded phase. Selection of the bonded phase depends on the pK or pA b of the target analytes. Sample cleanup using ion exchange is highly selective and can separate polar ionic compounds that are difficult to extract by the liquid-liquid partition technique. 

Section II covers the latest trends in reducing sample preparation time, including direct sample infusion/injection and on-line solid phase extraction (SPE). In Section III, we focus on newer trends in stationary phases and how these phases hope to offer different selectivities compared to current CIS-based phases. Section IV briefly provides a few observations on how new detectors are increasing the versatility of HPLC. Finally, in Section V we examine monolithic columns, small particles packed in short columns, high-temperature LC, ultra high-pressure LC, and parallel injection techniques. 

A contemporary of the method just described is the use of an absorbent (e.g. C-18) bonded onto granular or disk-type supports (solid-phase extraction [5]). The granular material is used in cartridge form (typically less than 5 ml), while disk forms are placed in a funnel/holder such as shown in Fig. 18.1b. A liquid (e.g. water, milk, or juice) would be passed through the cartridge (or filter disk), the analytes absorbed in the stationary matrix, the absorbent washed with water, and then the analytes of interest eluted from the absorbent with an organic solvent. This method has found limited use in the isolation of volatiles from foods but continues to find significant application in the analytical field overall [6]. 

Support materials for solid phase extraction (SPE) and for chromatographic techniques have been prepared by ROMP. pH-stable high capacity stationary phases have been prepared by copolymerization of functional monomers with a suitable crosslinking agent, with precipitation polymerization techniques. 

Solid-phase extraction uses a small volume of a chromatographic stationary phase or mole-cularly imprinted polymer23 (Box 26-2) to isolate desired analytes from a sample. The extraction removes much of the sample matrix to simplify the analysis. The opening of this chapter shows a solid-phase extraction membrane and extraction cartridges mounted on syringes. 

Actually, solid-phase extraction is used not only as a rough preliminary fractionation procedure. Prieto et al. described the complete fractionation of the total lipids from wheat into eight neutral lipid, two glycolipid, and four phospholipid classes in addition to PC and LPC, TV-acyl PE and A-acyl LPE were detected (37). However, two separate stationary phases (silica and aminopropyl) as well as seven different mobile phases were needed. Moreover, 14% crosscontamination of PC and LPC was observed, and the recovery of the phospholipids was limited to about 85%. Hence, SPE is a rapid and efficient technique for preliminary fractionation, but loses its advantages if more complex separations are tried. 

Cleanup An additional separation of the mycotoxin from lipids and other components of the matrix is accomplished through the cleanup step. Most procedures include solid-phase extraction on stationary phases such as silica, C,8, florisil, and phenyl. Prepacked columns are largely used, with the variations between lots being recently ameliorated. Alternatively, the use of cleanup by immunoaffinity, based on the formation of mycotoxin-protein conjugate, is on the increase, since this is very rapid, selective, and usefully employed in various food matrices. One disadvantage is that the cost is still rather high, and cross-contamination phenomena (false-positive) can occur (30). 

A novel multiresidue method has been developed for quantitation of TBZ, the metabolite 5-hydroxythiabendazole (5-OH-TBZ) in raw cow s milk. The 5-HS04-TBZ was hydrolyzed quantitatively under acidic conditions to 5-OH-TBZ. The TBZ and 5-OH-TBZ were extracted from milk at pH 8.0 with ethyl acetate, followed by cleanup of the extract on a cation-exchange solid-phase extraction column. Analytes were separated with a cation-exchange stationary phase ... 

The method commonly proposed is based on cation-exchange extraction followed by derivatization of the fraction of interest with OPA (46,55,98,99,114,124-126) (when isolating BAs in wines). Solid-phase extraction has been performed with several stationary phases based on anionic (113) or cationic (37,39) exchangers or octadecylsilane groups (38), as well as a combination of both (51). 

Up to now, most efforts have been directed towards the preparation of uniformly sized spherical MIP particles in the micrometre range. This is the obvious consequence of the need for this kind of materials as fillers for high-performance chromatographic columns, capillaries for electrophoresis, cartridges for solid-phase extractions and other applications requiring selective stationary phases. Additionally though, strategies for the preparation of other more sophisticated MIP forms, such as membranes, (nano)monoliths, films, micro- and nanostructured surfaces etc. 

Although potentially useful for sample preparation by solid-phase extraction, monolithic MIP phases had initially only been applied as stationary phase for LC... 

Aqueous samples may alternatively be extracted by solid phase extraction using reversed phase C-18 stationary phase column, such as Supelclean ENVI-18. The column must be conditioned with toluene-methanol (10 1), methanol, and deionized water, respectively, prior to sample addition. PAH analytes are eluted with toluene-methanol (10 1) mixture. 

The following table provides the most commonly used bonded phase modified silica substrates in solid phase extraction.1 Additional information on many of these materials can be found in the More Common HPLC Stationary Phases table in the HPLC chapter in this book. 

Another popular and selective extraction technique widely used in bioanalysis is solid phase extraction (SPE). SPE is a separation process utilizing the affinity of the analytes to a solid stationary phase. By manipulating the polarity and pH of the mobile phase, the analytes of interest or undesired impurities pass through stationary phase sequentially according to their physical and chemical properties. For a SPE procedure, a wash step refers to the elution of the unwanted impurities which are discarded and the elution step refers to the elution of the analytes of interest which are collected. While the fundamental remains the same in decades, the continuing invention and introduction of new commercial stationary phases and accessory devices have boosted the application of SPE in bioanalysis and many other fields. 

Using a solid, microporous membrane to define a stationary phase boundary during extraction may alleviate this problem. The feed solution and the extractant flow... 

An elegant study was presented by Thomas et al. who employed selective solid-phase extraction by immunoaffinity CEC (IACEC) to enhance detection limits. A model compound, fluorescein isothiocyanate biotin, was electrokinetically applied to a capillary column packed with an immunoaffinity stationary phase. The analyte was first selectively bound to the stationary phase, then eluted, migrated by zone electrophoresis, and detected by LIF [79],... 

The term solid-phase extraction was introduced by personnel of the J. T. Baker Company in 1982. The method consists of retention of the analytes from a liquid or gaseous sample to a solid stationary phase and subsequent removal of analytes using an appropriate eluent. The main purpose of SPE is isolation and preconcentration of compounds of interest or sample clean-up and simplification of the matrix. Application of this sample preparation technique also allows extract fractionation. As a result of significant reduction in the volume of organic solvents used, high recovery, and the possibility of process automation, SPE is a good alternative for conventional liquid-liquid extraction. According to their affinity for the compound of interest, stationary phases are classified as follows ... 

Glycerinic plant extracts have various application in the naturist medicine, but they cannot be analyzed directly by TLC due to the presence of glycerin which should be removed first from the sample [9]. Solid-phase extraction (SPE) is a fast and convenient method for the separation of glycerin. The organic compounds from the analyzed plant extract are retained in the SPE cartridge on a nonpolar stationary phase (usually silica-Cig) the glycerin and the nonse-lectively retained compounds are eluted with a polar mobile phase (can be a diluted solution of methanol in water). The retained compounds are eluted from the... 

Recently, solid phase extraction (SPE) on several stationary phases has been extensively used in the pre-... 

Naturally-occurring humic-metal complexes have been isolated from estuarine systems and seawater using solid phase extraction (SPE) onto a Cig HPLC column to preconcentrate the sample (JO-12). Samples were subsequently eluted from the SPE colunm at a much higher concentration and injected onto another HPLC column and detected by UV absorbance and a metal-sensitive detector, such as atomic fluorescence spectroscopy. The concentration of metal-humic complexes in natural aquatic environments was then calculated. However, there was some evidence of competitive binding of the metal ion between the organic matter and free silanol groups in the stationary phase resulting in a loss of metal in the column and erroneously low metal values (10). 

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