Solid phase extraction high-affinity phases

Volatile migrants pose a different sort of challenge. The usual evaporative concentration techniques will result in the loss of analyte. The analyte may be partitioned into a small volume of non-volatile solvent for subsequent analysis, but identification of a useful combination of solvent miscibility and analyte solubility is often impossible. Solid phase extraction and solid phase micro-extraction are often very useful for aqueous/ethanolic matrices. Here, a large volume of matrix is brought into contact with a small amount of solid material for which the analyte has a high affinity. The analyte is then desorbed from the solid phase with an appropriate solvent for subsequent analysis. 

Subramanian and coworkers developed polymeric sorbents using different support materials (such as Merrifield chloromethylated resin, Amberlite XAD 16) and complexing ligands (amides, phosphonic acids, TTA), and evaluated their binding affinity for U(VI) over other diverse ions, even under high acidities. The practical utility of these sorbents was demonstrated using simulated waste solutions (220-222). Shamsipur et al. reported the solid-phase extraction of ultra trace U(VI) in natural waters using octadecyl silica membrane disks modified by TOPO (223). The method was found satisfactory for the extraction and determination of uranium from different water samples. 

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 ... 

A wide range of chemical compounds have been imprinted successfully, ranging from small molecules,40 2 to large proteins and cells.43 MIPs have been developed for a variety of applications including chromatography,4445 solid-phase extraction (SPE),46 47 enzyme catalysis,48 sensor technology,44>49>50 biomimetic sensors,5153 and immunoassays.54-56 MIPs are robust, inexpensive and, in many cases, possess affinity and specificity that are suitable for industrial applications. The high specificity and... 

The arylurea hetbicides wete also used for MIPs synthesis. Two arylureas, fenuron and isoproturon, wete polymerized svith MAA as functional monomet and used as adsorbents for solid phase extraction of pollutants. The isoprotuton-imprinted polymer did not demonstrate the selectivity towards the template but had a high affinity towards all other arylurea herbicides. The corresponding blanks (nonimprinted polymers) did not retain any of these compounds, which suggest that the imptinting was achieved. With fenuron, very good specificity for this herbicide was observed. This result can be explained by the small size of the fenuron molecule. Indeed the other arylureas were not able to enter in the small cavities formed around fenuron due to steric interactions of the meta- or para-substituents in the aromatic ring. ... 

A steadily increasing number of publications report the use of phosphate-derived template molecules to prepare MIPs for solid-phase extraction (SPE). SPE involves the selective pre-concentration of trace-level compounds from complex mixtures. The high selectivities and affinities obtainable by molecular imprinting render these polymers ideal for use as SPE sorbents. 

For solid phase extraction, an ideal MIP adsorbent should have the following characteristics High binding affinity, specificity and capacity fast association and disassociation kinetics broad solvent compatibility and long-term stability. 

Molecular imprinting for solid phase extraction has attracted increasing interest in the past few years. MIP-based SPE is now considered to be the first commercialization effort to market the imprinting technology. As in other related applications, success in this aspect largely depends on the performance of MIP adsorbents under real conditions. In addition to strive for very high binding affinity and specificity, perhaps more important issues, but not so much foreseen by many of the research... 

High-performance affinity chromatography has recently been reported with trypsin-modified avidin supported on 5 pm silica. While the separations were successful and a wide range of foods were studied, elution times were 80 minutes and ADAM post-column reactions were still required (Hayakawa et al. 2009). However, such affinity columns within a solid-phase extraction (SPE) platform make realistic choices for sample preparation, whereby the biotin can be purified and concentrated prior to reversed-phase HPLC. R-Biopharm has recently developed a commercially available antibody-based immunoaffinity column to bind biotin from aqueous extracts, providing an excellent technique to clean up complex samples. 

A new tag strategy, termed syndiesis based on affinity separation (SAS) , was developed for high throiq)ut synthesis of organic conq)oimds. In this method, the desired tagged conq)ound was separated from the reaction mixture by solid-phase extraction using specific molecular recognition. The interaction between a crown ether (32-crown-lO) and ammonium ion and the interaction between a barbituric acid derivative and its artificial receptor were used for SAS. 

Several methods have been used to separate the lanthanides chemically solvent extraction, ion exchange chromatography, HPLC using Q-hydroxyisobutyric acid and, in limited cases, selective reduction of a particular metal cation.40-43 The use of di(2-ethylhexyl)orthophosphoric acid (HDEHP) for the separation of various rare-earth elements via solvent extraction has also been reported.44 16 This separation method is based on the strong tendency of Ln3+ ions to form complexes with various anions (i.e., Cl- or N03 ) and their wide range of affinities for com-plexation to dialkyl orthophosphoric acid. When the HDEHP is attached to a solid phase resin, the lanthanides can be selected with various concentrations of acid in order of size, with the smallest ion being the most highly retained. 

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. 

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