Solid-phase extraction operation

For a cassette containing structurally similar compounds (Table 1), it is possible to develop and use a high-throughput extraction approach such as deep-well liquid-liquid extraction or a deep-well solid-phase extraction operating under generic wash/elution conditions. These approaches do work for a majority of... 

Solid phase extraction systems have a wide range of application whether operated manually or automatically. Wherever materials are present in solution at very low concentrations they offer a means of extraction and concentration that is simple, efficient and fast. 

Regression correlation coefficient Regression coefficient of determination Rolling circle amplification Water solubility Sodium dodecyl sulfate Supercritical fluid extraction Standard operating procedure Solid-phase extraction Surface plasmon resonance Thymine... 

Application of SPE to sample clean-up started in 1977 with the introduction of disposable cartridges packed with silica-based bonded phase sorbents. The solid phase extraction term was devised in 1982. The most commonly cited advantages of SPE over liquid-liquid extraction (LLE) as practiced on a macroscale include the reduced time and labor requirements, use of much lower volumes of solvents, minimal risk of emulsion formation, selectivity achievable when desired, wide choices of sorbents, and amenability to automation. The principle of operation consists of four steps (1) conditioning of the sorbent with a solvent and water or buffer, (2) loading of the sample in an aqueous or aqueous low organic medium, (3) washing away unwanted components with a suitable combination of solvents, and (4) elution of the desired compound with an appropriate organic solvent. 

Samples rarely come in a form that can be injected directly into the instrument some form of sample preparation usually is required. Sample preparation includes any manipulation of the sample prior to analysis, including techniques such as weighing, dilution, concentration, filtration, centrifugation, and liquid- or solid-phase extraction. Sample preparation can be performed either on-line or off-line, but it is usually performed offline. Off-line preparation can be time-consuming and tedious, and the more steps that are required, the more susceptible the analytical method is to operator error and irreproducibility. 

It is too often assumed that because precolumn sample preparation devices, such as solid-phase extraction cartridges, are simple tools, they require relatively little skill or attention to detail for successful use. Cartridges do, however, require attention to detail for successful operation in sample enrichment procedures. Two of the most important parameters to control and understand are flow-rate effects and recovery (or loadability) effects. 

To illustrate potential problems that may occur with real samples, the effect of flow rate was investigated. To demonstrate this effect, riboflavin was trace-enriched from 10 mL of an aqueous solution. A fresh solid-phase extraction device was properly conditioned and used for each experiment. The surface of the solid phase must be solvated so that the cartridge can be properly conditioned. Directions for solvating the surface can be found in the operating instructions that accompany the cartridge. 

Figure 1 Schematic illustrations of micro unit operations (a) mixing and reaction (b) solvent extraction (c) phase separation (d) two-phase formation (e) solid-phase extraction (f) heating (g) cell culture.

Clinical analysis of certain biological markers in urine, including ascorbic acid (1), is very important. An automatic method for solid-phase extraction coupled to CE with DA-UVD was developed and optimized, including autosampling and post-run operations to restore the instrument to readiness for the next sample. The whole cycle lasted 13.01 min, thus allowing the simultaneous determination in urine of creatine (34), creatinine (35), uric acid (3), p-aminohippuric acid (36) and l" . ... 

After leaving the preparation process, the flakes (or collets) are delivered to the solvent extraction operation. As this process typically uses a flammable solvent (and is classified as a hazardous flammable environment), the operation is usually somewhat removed from other facilities, and access to the controlled area is restricted. Figure 5 illustrates the typical unit operations associated with solvent extraction, which include extraction, solvent distillation, and liquid-phase recovery. Upon discharge from the extractor, solid-phase extracted material is desolventized, toasted, dried, and cooled prior to meal finishing. 

The most simple and common workstations are those for dilution and/or reagent addition to a number of samples in a simultaneous manner, either to all samples in a rack or to a line with a slide z-axis (as in the Biomex" 2000 model from Beckman). Most workstations are designed to operate with liquid samples such is the case with those from Cyberlab, Gilson, Zymark, SciLog, Sagian, Beckman and Hamilton, which manufacture specific equipment for liquid handling, solid-phase extraction and preparation of liquid... 

In a limited version, only the most critical stages are automated by the use of robots with limited, strictly defined movements examples are automated processes of solid-phase extraction (SPE), heating, and mixing. The robots are controlled by a computer and the operator chooses the suitable values of the parameters from given ranges (e.g., autosampler). 

Manoli and Samara, 1999) or capillary electrophoresis (Martinez et al., 1999). All these methods require sophisticated and expensive instruments which are difficult to transport and to adapt for on-site operation or for field monitoring. Moreover, these methods normally include an extraction step (liquid-liquid or solid phase extraction) for which a complex calibration process is needed to account for the appreciable loss of analyte (Thurman and Mills, 1998 Simpson, 2000) that occurs during the process. Further, they involve the use of organic solvents including halogenated compounds on whose use there are legal limitations (US EPA, 1998). 

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