Solid phase extraction defined

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). 

Solid phase extraction is used primarily to prepare liquid samples and extracts of semi-volatile or non-volatile analytes, but may also be used for solids pre-extracted into solvents. The choice of sorbent is the key factor in SPE, because this can control parameters such as selectivity, affinity, and capacity. This choice depends primarily on the analytes and their physicochemical properties, which should define the interactions with the chosen sorbent. However, results also depend on the kind of sample matrix and interactions with both the sorbent and the analyte. SPE sorbents range from chemically bonded silicas, such as with the C8 and C18 organic groups, to graphitized carbon. 

GC, preferably with MS coupling and sample preparation (extraction, purge trap, spray trap, solid phase extraction (SPE), solid phase microextraction, headspace, thermodesorption, soil air trap], nondispersive infrared spectroscopy (NDIR). FT-IR, TLC, immunoassays and biosensors (for determination of defined substances)... 

The hydrophobic properties of a series of 5-aIl l-, 5-alkenyl- and 5-alI yl-substituted deoxyuridines were defined from their retention behaivour on silica and reversed-phase columns. Zeatin and its riboside were determined in plant tissues by solid-phase extraction and cation-exchange h.p.l.c. Sugar and nucleoside H-phosphonates have been separated by anion-exchange h.p.l.c., and by flow injection analysis in which the components are hydrolysed, oxidised and the orthophosphate so generated is detected colorimetrically. ... 

A distribution ratio can also be defined for solid phase extraction, i.e. 

A challenging task faced by the analytical chemist when dealing with raw samples is extracting/isolating the analyte of interest from the sample matrix. It is fair to say that the majority of nonideal samples arrive in a format incompatible with most analytical instrumentation, and requires some degree of clean-up. Even well-defined samples (e.g. aqueous solutions) require basic filtration prior to analysis. Other desirable techniques may include liquid/liquid extraction and solid phase extraction. 

The terms of the fractions are more likely to be operationally, rather than chemically, defined. However, each extractant in the sequentially selective procedure mostly targets one major solid-phase component. Therefore, trace elements bound to the targeted fraction can be either... 

Indeed the overall effect of such chemicals on the surface chemistry of soils and sediments remains poorly understood. Despite the difficulties this type of technique is still widely used. As with many operationally defined methods, it is difficult to make direct comparisons between independent studies however, for individual studies sequential extraction can play a useful role in an overall programme of study regarding the chemical forms of radionuclides bound to the solid phase under different environmental conditions so long as it is realised that in this type of study the species are themselves really defined by the nature of the extraction system employed (see Chapter 10). 

Solid-phase microextraction (SPME) is a fast and solventless modification of SPE techniques [20]. SPME involves the use of fiber (fused silica fiber or polymer-coated fused fiber) coated by an adsorbent. The method is applied for extraction of different kinds of both volatile and nonvolatile analytes from different kinds of media, which can be in liquid or gas phase. In the direct extraction mode, coated fiber is immersed in the sample for a defined time, until equilibrium between the sample matrix and the solid phase is reached. The analyte is transported by diffusion directly to the extracting phase. In the next stage, the compound of interest... 

Methods of Speciation and Fractionation. It is apparent that in order to understand the mobility of arsenic and its availability for reactions, methods of speciation and fractionation must be applied to sediment samples in field and laboratory studies. In this paper speciation refers to the separation and quantitative determination of inorganic arsenic, methanearsonic acid, and cacodylic acid. Compartmentalization involves identifying the major compartments for arsenic in a heterogeneous system (e.g. aqueous, adsorbed, occluded,...) and determining the amounts of arsenic in each compartment. Fractionation involves the extraction of arsenic from operationally defined fractions of the solid phase of an aquatic system (e.g. sediment). 

Because the SEDEX scheme, like all sequential extraction schemes, is operationally defined, it is important to obtain corroborating evidence for the identity of the separately quantified sedimentary phosphorus reservoirs whenever possible. This can be accomplished by analyzing pore-water chemistry and other solid-phase components of the host sediments, and by linking depth profiles of various solutes and components to SEDEX phosphorus profiles. Some of the most elegant and comprehensive work of this type has been done by... 

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