Solid-phase extraction cleanup applications

Solid-phase extraction techniques that are based mostly on reversed-phase (Cis) sorbents, have been also widely used for cleanup and concentration purposes (23, 25, 27, 31, 34, 37, 46, 51, 52, 55, 65). However, many applications have indicated that cleanup using these nonpolar materials may not be very effective in removing interfering substances from sample extracts. Hence, polar sorbents such as silica (23, 26, 29, 30, 32, 40, 42, 44, 52, 53) or Florisil (45) have been also suggested as more powerful alternatives for the isolation and/or cleanup of amphenicols. 

Solid-phase extraction seems to be more suitable for multiresidue cleanup. This procedure has become the method of choice for isolation and/or cleanup of -lactam antibiotics from biological matrices, because it requires low solvent consumption, it is generally less time-consuming and labor-intensive, and offers a variety of alternative approaches that allow better extraction of the more hydrophilic -lactam antibiotics such as ampicillin. It is usually performed using reversed-phase Ci8 (69-71, 80-83, 90, 92-94, 99, 107, 112-116, 121-125) or Cg (103), anion-exchange (95, 124), and polar diol (95) or alumina (101, 113) sorbents. In recent applications, some workers demonstrated the potential of online solid-phase extraction in the determination of monobasic penicillins in bovine muscle tissues using a reversed-phase Cis 5 m cartridge and an automated... 

To reduce coextractives in the primary sample extract and concentrate the analyte(s), various types of sample cleanup procedures can be applied. They include conventional liquid-liquid partitioning, solid-phase extraction, matrix solid-phase dispersion, and online dialysis and subsequent trace enrichment (Table 29.5). In many applications, more than one of these procedures is applied in combination to decrease the background noise of the detector, thus making it possible to quantify trace level residue concentrations. 

Cleanup by solid-phase extraction has also been widely employed since it is a simple, fairly inexpensive, and easy-to-perform procedure for purification of the crude extract. The use of disposable solid-phase extraction columns is currently part of most, if not all, modern analytical methods for the determination of anthelminthics in biological matrices at residue levels. Both normal-phase columns based on silica (333-335, 340, 367, 372), alumina (346, 373-375), or aminopropyl (339, 365, 370) materials, and reversed-phase columns based on Ci8 (319, 323, 324, 328, 344, 346, 347, 349-351, 357-359, 364, 367) and cyclohexyl (329, 332, 360) sorbents have been described in analytical applications. 

The solvent extracts can be cleaned up by traditional column chromatography or by solid-phase extraction cartridges. This is a common cleanup method that is widely used in biological, clinical, and environmental sample preparation. More details are presented in Chapter 2. Some examples include the cleanup of pesticide residues and chlorinated hydrocarbons, the separation of nitrogen compounds from hydrocarbons, the separation of aromatic compounds from an aliphatic-aromatic mixture, and similar applications for use with fats, oils, and waxes. This approach provides efficient cleanup of steroids, esters, ketones, glycerides, alkaloids, and carbohydrates as well. Cations, anions, metals, and inorganic compounds are also candidates for this method [7],... 

While it is wonderful to be able to inject neat samples directly, sample preparation can often improve selectivity and sensitivity. If the resolution is poor, the salt content of the sample too high, or the capillary fouls, consider a sample cleanup. This can include liquid-liquid extraction, solid-phase extraction, supercritical fluid extraction, protein precipitation, or dialysis, depending on the solutes and application [38]. The final sample diluent should be a solution that is CE-Mendly. That usually means low ionic strength compared to the BGE. 

SPE is used widely for the cleanup and concentration of analytes for analysis using LC, HPLC, and LC-MS, discussed in Chapter 13. As you will see, the phases used in HPLC for the separation of compounds are in many cases identical to the bonded solid phase extractants described here. Detailed examples and applications notes are available from a number of SPE equipment suppliers J.T. Baker (www.jtbaker.com), Supelco (www.sigma-aldrich.com/supelco), and Phenomenex (www.phenomenex.com) are a few of the companies that supply these products. 

As illustrated by the examples given in Table 3, the application of labs-on-chips to real samples is still limited. This is partly due to the fact that the analytical assay is only the final step of the whole procedure, which includes sample pretreatment protocols such as filtration, analyte cleanup, or analyte preconcentration. However, also the integration of corresponding microfabricated elements is described. Filtration was achieved by porous membranes or arrays of thin channels preventing particulates to enter the analytical device. Analyte preconcentration in combination with removal of other sample constituents is achieved by solid-phase extraction modules, which are either capillaries or beads coated with a suitable adsorbent, such as a Cl 8 phase originating from coating with octa-decyltrimethoxysilane, from which the analyte is... 

Solid-phase extraction (SPE) and elution with different mixtures of solvents are also very common [24,73,128,153]. XAD-2 [9,10,14—16,68,80,81,90-92,135,142], polyurethane foam [68,80], and C18-bonded silica [14,31,141] are the most widely used adsorbing resins. The adsorbing material is generally supported inside a column or fixed on a membrane disk. SPE has several advantages, in fact it can be used in field applications, it has easy automation, a low solvent consumption, and there is less critical cleanup of the eluate. 

Solid-phase extraction (SPE) can be used to separate an organic analyte from the aqueous phase and to concentrate the analyte in a few milliliters of solvent. SPE also can be used to clean up a sample matrix and remove concomitant contaminants from the analyte. In some cleanups the analyte is absorbed onto the solid phase and the interferences pass through unretained. In the opposite cleanup strategy the solid phase retains the interferences and allows the analyte to pass through the cartridge with the mobile phase. In some environmental application, SPE performs all three roles—extraction, concentration, and cleanup. 

LC/MS/MS assay for 13 commonly prescribed pain management drugs from urine with cleanup using solid phase extraction (SPE). Phenomenex Application TN-1070... 

Solid-phase extraction (SPE). In solid-phase extraction, the analytes are retained on short, disposable cartridges packed with microparticulate adsorbents or bonded phases. After sample application, the minicolumns are washed with a solvent to remove poorly retained matrix components, followed by displacement of the analyte(s) with a strong solvent. SPE may be used as a cleanup... 

Isolation can be performed by liquid-liquid extraction (LLE) at a pH at which the analyte is nonionized or by solid-phase extraction (SPE) preceded or followed by cleanup steps. Sample pretreatment for SPE depends on the sample type whole blood and tissue (homogenates) need deproteinization and filtration/ centrifugation steps before application to the SPE columns, whereas for urine usually a simple dilution step and/or centrifugation is satisfactory. Whatever SPE column is used, the analyst should keep in mind that there are large differences from batch to batch, and that the same sorbents from different manufacturers also... 

Direct injection of blood serum (102) or sample extracts with little or no cleanup (53) is possible, which makes HPLC procedures comparable in speed with other rapid tests With increased use of solid-phase absorption in cleanup, automation of procedures is feasible TLC is also a useful and inexpensive technique and quantitative TLC methods have been described (30,63) The following chapter describes practical application of various procedures in a drug residue monitoring program ... 

Immunoaffinitv assay The Irnmunoaffinity assay which Involves the use of an antibody column that traps the mycotoxins has been used for AFBl, AFMl and OTA (8, 9, 13, 36, 83,84). The toxin can be then eluted from the column for subsequent analysis or adsorbed In a solid-phase to which the fluorescence Is then read directly. Thus, the affinity column serves as a specific cleanup and concentration tool for the analysis. Recent advances In Improvement of Instrumentation of fluorescence detection and post-column derlvatlzatlon have led to a wider application of this method for AF detection. An AOAC collaborative study showing good result has been completed (85). In such an assay, AF extracted from the sample Is first diluted with buffer at pH 7.0 and then subjected to a disposable affinity column containing antl-AF antibody Sepharose gel. After washing, AF Is removed from the column with methanol, subjected to treatment with Iodine solution, and the fluorescence determined. Nevertheless, this method cannot be used for mycotoxins, such as TCTCs, which do not have high fluorescence or a chromophore. 

Other methods, such as matrix solid-phase dispersion (MSPD) have also been applied in sample pretreatment. Among other applications, MSPD was recently used for the analysis of seven flavonoids in citrus juice [56] or 18 flavonoids from Ginkgo biloba tablets combining extraction and cleanup in a single run [57]. 

---