Solid phase extraction adsorbants used

A cleanup procedure is usually carried out to remove co-extracted matrix components that may interfere in the chromatographic analysis or be detrimental to the analytical instrument. The cleanup procedure is dependent on the nature of the analyte, the type of sample to be analyzed, and the selectivity and sensitivity of the analytical instrument used in the analysis. Preliminary purification of the sample extracts prior to chromatographic separation involves liquid-liquid partitioning and/or solid-phase extraction (SPE) using charcoal/Celite, Elorisil, carbon black, silica, or aminopropyl-silica based adsorbents or gel permeation chromatography (GPC). 

Zhou, Q., J. Xiao, and W. Wang. 2006. Using multi-walled carbon nanotubes as solid phase extraction adsorbents to determine dichlorodiphenyltrichloroethane and its metabolites at trace level in water samples by high performance liquid chromatography with UV detection. J. Chromatogr. A 1125 152-158. 

Stationary phases (silica, reversed phases, Amberlite, and Sephadex) or by solid-phase extraction techniques using different adsorbents, which in the last decade has been found very convenient for the isolation of flavonoids from complex matrices. 

In a solid-phase extraction the analytes are first extracted from their solution matrix into a solid adsorbent. After washing to remove impurities, the analytes are removed from the adsorbent with a suitable solvent. Alternatively, the extraction can be carried out using a Soxhlet extractor. 

The solid phase extraction cartridge (SPEC) is another somewhat vainglorious name given to a short inert plastic tube packed with an adsorbent, usually a reversed phase or an ion exchange resin. The particle size of the packing is often significantly larger than that used... 

Fig. 18.1 Systems used to absorb aroma compounds from samples for analytical purposes, a Traps loaded with various adsorbents [4]. b Solid-phase extraction (disk in a holder assembly) [5]. c Solid-phase microextraction (coated needle inserted in sample) [5]. d Twister (1 -cm length) [4]. (Courtesy of GERSTEL GmbH and Co. KG)...

A fourth conclusion, based on the advantages of the use of solid adsorbents, is the gradual replacement of solvent extractions with solid phase extractions. The movement toward this replacement is already evidenced by the commercial availability of several different cartridges of bonded phases and high-surface-area synthetic polymers. 

Besides solid-phase extraction, column chromatography is also often used for cleanup and purification of polyphenolics from plant material. Ionic adsorbants (polyvinylpyrrolidone or PVP, polyamides, and Sephadex LH-20) and Amberlite XAD-2 resin have been used to isolate and purify polyphenolics from crude extracts. For the separation of polyphenolics from plant material, column chromatography using Sephadex LH-20, a gel-filtration matrix, is often used with various eluting solvents (Park and Lee, 1996). The most widely used solvents for column chromatography are aqueous methanol and aqueous ethanol. 

Solid-phase extractions (SPE), in which DOM is selectively concentrated on a solid-phase extractant such as XAD-2 resin or Ci8 adsorbent. In these methods, both inorganic solutes and water are removed concurrently, and a suitable solvent is used to desorb the concentrated, desalted DOM from the solid-phase extractant. In principle, all inorganic solutes may be removed by SPE. 

After several decades of research, fundamental aspects of the chemical composition and structure of marine organic matter remain elusive. Advances in the chemical characterization of marine organic matter are, in large part, dependent on the development of quantitative methods for its concentration and isolation from seawater. Each of the major methods currently used for the isolation of marine DOM recovers around one-third of the DOM in seawater (solid-phase extractions, using XAD resins or C18 adsorbents, and ultrafiltration). A coupled reverse osmosis-electrodi-alysis method has recently been used to recover an average of 75% 12% of marine DOM from 16 seawater samples however, the method has emerged too recently to have been well tested at this time. 

Analytes may accumulate in the sorption phase either by adsorption onto the surface of solid sorbent materials or by absorption in absorbent liquids or polymers that behave like subcooled liquids.The advantage of solid adsorbents is the potential to select materials with a high affinity and selectivity for target analytes. However, the sorption capacity of adsorbents is usually limited, and the description of adsorption/desorption kinetics of analytes to adsorbents is complex. Typically, the adsorbent materials used in passive samplers are similar to those used in solid-phase extraction techniques. 

Maurer has reviewed the application of LC-MS and LC-MS/MS to the detection of alkaloids in human biofluids [14]. Extraction techniques include liquid-liquid extraction relying upon the ionization of alkaloids in aqueous acid, solid phase extraction (SPE) in which alkaloids are cleaned up and concentrated from the biomatrix by adsorption and subsequent elution from a small cartridge of solid phase adsorbent, and solid-phase microextraction (SPME), in which analytes are adsorbed directly from the matrix or the headspace above the heated matrix onto a fine fiber of adsorbent on fused silica. The latter process is more commonly used with GC-M S but is finding increasing use with LC-MS. 

An alternative to liquid-liquid extraction is solid-phase extraction (SPE). With SPE a liquid sample is introduced into the top of a plastic syringe shape column containing a small amount (often 100- 500 mg) of a selective adsorbent (Figure 8.1). The adsorbents are of the same types as used for HPLC, typically silica, or bonded silica such as Cl 8, C8, C5, C2, cyano, phenyl, diol and ion-exchange materials. The properties of the adsorbents are similar to HPLC columns and so the same principles apply for retention and desorption of analytes. 

Solid phase extraction. With the availability of pre-prepared cartridges of silica-based adsorbents, the use of solid phase extraction has increased in the last few years although the technique has been in use for many years for the isolation of many biochemicals, e.g. amino acids, catecholamines. In essence it is a version of chromatography conditions for the selective adsorption of the analytes (column, solvent, pH, etc.) are chosen, the sample is applied to a column, washed and the analytes selectively eluted with appropriate solvents. Since the columns are disposable there is no need to worry about protein contamination or infection. The adsorbents available cover an even wider range than HPLC materials since they are not required to withstand high back pressures. It is possible... 

Water. PCBs are non-polar compounds and consequently they are highly soluble in non-polar solvents this makes their extraction easier from water samples with nonpolar immiscible solvents. -Hexane and dichloromethane, or a mixture of them, are the most widely used solvents in liquid-liquid extraction techniques (1, 16, 29-31). Solid Phase Extraction (SPE) and elution with different mixtures of solvents (i.e., acetone/hexane/ dichloromethane) is a very attractive alternative to the liquid-liquid one (29, 32, 33). When large volumes of samples need to be collected, water can be pumped directly through a system containing an adsorbing material suitably supported, i.e., XAD-2, XAD-4, Tenax, C18, CI8-NH2, etc. It can be... 

Solid-phase extraction (SPE) is an alternative to LLE. In SPE the analytes are partioned between a solid and a liquid [57, 58], Generally, interfering compounds are rinsed off the solid adsorbent and the analytes are then desorbed with an eluting solvent [58], A range (e.g., normal-phase, reversed-phase, ion exchange, restricted access) of sorbents and formats are available for SPE and the SPE systems are easy to automate [59, 60], In order to accomplish the isolation of the products from the fermentation matrix, both SPE and LLE were evaluated for use in papers I and II. 

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