Solid-phase microextraction recovery

Solid-phase microextraction (SPME) consists of dipping a fiber into an aqueous sample to adsorb the analytes followed by thermal desorption into the carrier stream for GC, or, if the analytes are thermally labile, they can be desorbed into the mobile phase for LC. Examples of commercially available fibers include 100-qm PDMS, 65-qm Carbowax-divinylbenzene (CW-DVB), 75-qm Carboxen-polydimethylsiloxane (CX-PDMS), and 85-qm polyacrylate, the last being more suitable for the determination of triazines. The LCDs can be as low as 0.1 qgL Since the quantity of analyte adsorbed on the fiber is based on equilibrium rather than extraction, procedural recovery cannot be assessed on the basis of percentage extraction. The robustness and sensitivity of the technique were demonstrated in an inter-laboratory validation study for several parent triazines and DEA and DIA. A 65-qm CW-DVB fiber was employed for analyte adsorption followed by desorption into the injection port (split/splitless) of a gas chromatograph. The sample was adjusted to neutral pH, and sodium chloride was added to obtain a concentration of 0.3 g During continuous... 

More recently, solid phase microextraction (SPME) [22] has been applied to the analysis of bug pheromones, using two techniques. In the first, headspace volatiles are trapped on the SPME fiber, analogous to trapping on SuperQ [e.g., 23]. Alternatively, if the source of the pheromone is known, the SPME fiber can be wiped on the cuticle to directly adsorb the compounds [24]. In either case, the fiber is then thermally desorbed directly into a GC or GC-MS. Whereas this method is excellent for analysis, with good recoveries, it does not provide a sample that can be used for bioassays or for isolation of an active compound. 

The fabrication of imprinted monolithic solid-phase microextraction fibres has been developed for the selective extraction and preconcentration of diacetylmorphine and its structural analogues, triazines, bisphenol A, anaesthetics, and antibiotics followed by GC or HPLC analysis [156,163,179,196,197]. In addition, the on-line coupling of the imprinted monolith as a preconcentration column with a conventional analytical column has been proposed for the enrichment and cleanup of environmental and food samples [163]. However, at present, the capacity of the imprinted fibres and thus the degree of recovery of analytes are very variable and obviously need some improvement. For example, the recoveries of triazines after SPME with an imprinted monolith prepared by in situ polymerisation of MAA as... 

Combination of static subcritical water extraction and solid-phase microextraction Comparison of CHC1F2, N2O and CO2 extractants. CHC1 F2 gave highest recovery, methanol-modified CO2 gave 90% recovery Combination of supercritical fluid extraction with off-line Fourier transform infrared spectroscopy... 

Extraction is the process of transferring a substance from a solid to a liquid phase or from a liquid to another liquid phase (immiscible with the former). From a practical viewpoint, the process can be achieved by leaching, which is transfer of compoimds from a solid phase to a solution (solid-liquid extraction, SEE) or by extraction via direct (liquid-liquid extraction, LEE) or indirect (SPE or solid phase microextraction, SPME) transfer of a substance from one liquid phase to another [75]. The efficiency of the extraction process is expressed as the percentage of extraction, which takes into accoimt the affinity of the investigated compoimds for both phases. In practice, a commonly used concept is that of recovery, understood as the degree of transition of a substance from one phase to another, expressed as a percentage. There are multiple methods for determining recovery. They can be divided into two classes ... 

Furton, K. G., et aL "Application of Solid-Phase Microextraction to the Recovery of Explosives and Ignitable Liquid Residues from Forensic Specimens." Journal cf Chromatography A. 97 (2000), 419-423. 

Solid-phase microextraction (SPME) is well documented with respect to its convenience and applicability to sampling volatiles and as an extraction technique to detect ignitable liquid residues when coupled with GCMS (185-188). Nonetheless, fire debris analysts have yet to widely adopt SPME as a viable alternative to the activated charcoal passive headspace technique. SPME is a simple, solventless extraction procedure in which a phase-coated fused-silica fiber is exposed to the headspace above the fire debris packaged in a closed container. A drawback to the procedure requires a rubber sleeve septum be placed at the opening of the container for maximum recovery of analytes. The technique has been applied successfully for the detection of flammable and combustible liquid residues on human skin (189). 

Today, sample preparation is maybe the step that most influences the accuracy of the whole analytic method, with the extraction of pesticide residues from environmental matrices the key factor for achieving it. There is no question that in the first decade of the century, SPE technique [72] is the most employed alternative to the classical solid-liquid [13] and liquid-liquid [14] extractions. These classical techniques present multiple disadvantages such as the low recovery of polar pesticides and transformation products (in the case of liquid-liquid extractions) and use of large volumes of solvents. Furthermore, several variants emerged based on the SPE technique solid-phase microextraction (SPME) [72-74], in-tube solid-phase microextraction [72,75,76], matrix solid-phase dispersion [72,77,78], and stir-bar sorptive extraction [72,79]. 

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