Solid phase extraction coatings

A solid-phase extraction in which the solid adsorbent is coated on a fused-silica fiber held within a syringe needle. 

Solid phase extraction (SPE) is a very simple, rapid and reproducible cleanup technique that is now widely accepted as an alternative to the time-consuming liquid-liquid extractions. Additionally, SPE uses relatively small volumes of solvents, and is easy to automate. It is available in a number of different formats, including cartridges, disks, loose material, well plates or SPME using film-coated capillaries. SPE can be considered as an extraction technique when used for isolation and concentration or a cleanup technique when used to remove co-extractives from solvent extracts. The use of SPE for cleanup is discussed later. 

When using PFT with a neutral selector, it is quite difficult to avoid any entrance of the chiral selector into the ionization source, particularly at a high pH, where EOF is important. The use of BGE at low pH and/or coated capillary to minimize EOF is therefore mandatory. However, the coaxial sheath gas, which generally assists the ionization process, leads to an aspirating phenomenon of the chiral selector in the MS direction. Javerfalk et al. were the first to apply PFT with a neutral methyl-/i-CD for the separation of racemic bupivacaine and ropivacaine with a polyacrylamide-coated capillary and an acidic pH buffer (pH 3). Cherkaoui et al. employed another neutral CD (HP-/1-CD) with a PVA-coated capillary for the analysis of amphetamines and their derivatives. To prevent a detrimental aspiration effect, analyses were carried out without nebulization pressure. Numerous other studies presented excellent results such as the enantioselective separation of adrenoreceptor antagonist drugs using tandem mass spectrometry (MS/MS) the separation of clenbuterol enantiomers after solid-phase extraction (SPE) of plasma samples or the use of CD dual system for the simultaneous chiral determination of amphetamine, methamphetamine, dimethamphetamine, and p-hydroxymethamphetamine in urine. 

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)...

Both liquid-phase and solid-phase extractions have been used for sample preconcentration or cleanup. For instance, an OTS-coated glass channel was employed for liquid-phase extraction, leading to an enrichment of samples (the... 

Sample pre-concentration was also achieved based on solid-phase extraction. This was carried out on ODS-coated silica beads (of diameter 1.5 1 4m) trapped... 

Dynamic Solid Phase Extraction The technique of dynamic solid phase extraction (SPDE) can be regarded as similar to NTD, where the rimer wall of the needle is coated with polymer. Lipinski introduced such a concept and attached a short section of metal capillary column coated with typical PDMS polymer to a gas-tight syringe [87]. The SPDE system is presented in Fig. 14.7 [88]. 

In most cases, chromatography and solid phase extractions with MIPs are performed with organic eluants. The rigidity of the backbone structure is critically important when considering the mechanical stress that occurs during HPLC separations. The macroscopic polymer beads are optimised with regards to monodisper-sity and mechanical stability. GC on the other hand relies on thermally stable coatings. 

In summary, non-covalently imprinted polymers offer a universal tool for sensor technology, besides the main applications in HPLC and solid phase extraction. The examples discussed above are but a few of the potential applications of smart chemosensory devices coated with non-covalent MIPs. The strategy of non-covalent imprinting is highly appropriate for sensory applications. Antibody-like... 

Solid-phase extraction devices and applications are evolving rapidly, and novel techniques that stretch the classical definition of SPE are becoming routine. Pawliszyn introduced solid-phase micro extraction (SPME) in 1989,5,14 and a commercial apparatus is available from Supelco (Bellefonte, PA). The SPME apparatus is merely a modified syringe that houses a fused silica optical fiber coated with an immobilized polymer film. The fiber can be exposed for extraction and then retracted for insertion or removal from the sample vial or instrument. Both manual and autosampler devices are available and each can be adjusted for proper fiber depth. Several coatings are available with varying thickness including polydimethylsiloxane, polyacrylate, polydimethylsiloxane/divinylbenzene, and carbowax/divinylben-zene. In contrast to SPE, which is an exhaustive extraction approach, SPME will extract only a fraction of an available analyte, hence it is not suitable for the isolation of impurities and degradants in most applications.15... 

Recovery and Analysis of Abamectin Residues. Sample preparation was a modification of the initial steps of Merck Co. Method 8001 (9). Cg solid-phase extraction columns (Fisher Prep-Sep, 300 mg resin) were conditioned by consecutive washes with hexane, ethyl acetate, methanol, acetonitrile, and water (20 ml. each). Samples (100 ml of glass-distilled water) were spiked with various amounts of abamectin, adjusted to 25% (v/v) acetonitrile, and applied to the columns. The columns were washed with 10 ml of water, and then the abamectin was eluted in 12 ml of acetonitrile. The eluates were evaporated to 1.0 ml at 70s under nitrogen. Dilutions of these samples were made in PBS-Tween-20% acetonitrile, and mixed with equal volumes of MAb B11C2.1 (1 200 in the same buffer) in sealed 1.4 ml polypropylene tubes. After incubation for 2 hr to about 14 hr (overnight) at room temperature, replicate aliquots (100 pi) were transferred to Immukm 2 EIA wells coated with 25 ng ivermectin 4"-hemisuccinate-CON for the standard competition EIA. Standard curves consisted of 8 dilutions of abamectin, from 0.01 ppb to 500 ppb, in triplicate. 

Solid-phase extraction, or liquid-solid extraction, can overcome several of these problems. Solid-phase extraction techniques use membranes or small disposable syringe-bairel columns or cartridges. A hydrophobic organic compound is coated or chemically bonded to powdered silica to form the solid extracting phase. The compounds can be nonpolar, moderately polar, or polar. For example, an octadecyl (C jj) bonded silica (ODS) is a common packing. The functional groups bonded to the packing attract hydrophobic compounds in the sample by van der Waals interactions and extract them from the aqueous solution. 

These imprinted micro spheres can then be packed more efficiently into chromatography columns or into solid-phase extraction (SPE) cartridges than the particles prepared by bulk polymerization techniques. Larger spherical imprinted polymer particles can be prepared by modification of preformed latex particles either by reswelling with a secondary polymerization mixture or by coating a spherical core particle with an imprinted polymer shell. 

As a result of the increase in the number of laboratories carrying out environmental analysis and the corresponding increase in the volumes that are used primarily for extraction and have to be disposed of, there has been increasing use of solid-phase extraction (SPE) methods including solid-phase microextraction (SPME) procedures using fiber-coated poly(dimethylsilox-ane), methyl silicone, or polyacrylate. These procedures are discussed in Sections 2.2.4 and 2.2.7. 

One more trend that is worth mentioning is the miniaturization of sample preparation techniques. Solid phase microextraction is one good example of where very small samples are consumed and very small extracts are produced. Solid phase extractions can also be scaled down by reducing the bed volume or by use of coated membranes. Likewise liquid-liquid extractions can be scaled down conserving both sample and solvent. 

Besides choosing the appropriate Ab, the assay method can be designed or manipulated to improve assay specificity using (a) protein precipitation, (b) liquid/liquid or solid-phase extraction, (c) HPLC separation of the analyte from the interfering compounds, (d) sample dilution with buffer or control matrix, or (e) an affinity solid phase (e.g., antibody-coated microtiter plate or polystyrene beads) to capture the analyte followed by wash steps. Affinity-purified antibodies and protein blockers are used in EIA to decrease nonspecific binding in plate assays. Increasing incubation time to reach equilibrium also improves binding specificity. 

---