Preconcentration solid-phase extraction

Sample Preconcentration/Solid-Phase Extraction. A microfluidic device with an external EOF... 

Two examples from the analysis of water samples illustrate how a separation and preconcentration can be accomplished simultaneously. In the gas chromatographic analysis for organophosphorous pesticides in environmental waters, the analytes in a 1000-mL sample may be separated from their aqueous matrix by a solid-phase extraction using 15 mb of ethyl acetate. After the extraction, the analytes are present in the ethyl acetate at a concentration that is 67 times greater than that in... 

ATOMIC ABSORPTION DETERMINATION OF Cu(II), Cd(II), Zn(II), Pb(II) USING PRECONCENTRATION BY SOLID-PHASE EXTRACTION ON PROPYLTHIOETHYLEAMINE MODIFIED... 

In order to one of the most effective separation and preconcentration procedure in trace metal analysis is solid phase extraction (SPE) of analyte. 

In recent decades the development of preconcentration steps to be implemented prior to analytical determinations of trace level compounds has been explored in considerable depth. With a view to eliminating or at least minimising the use of organic solvents used in conventional liquid-liquid extraction, other methodologies have been developed, such as membrane extraction, solid-phase extraction, solid-phase microextraction, etc. 

Riu et al. [542] has reported the determination of linear ethyl benzane-sulfates in coastal waters using automated solid-phase extraction followed by capillary electrophoresis with ultraviolet detection, and confirmed by capillary electrophoresis-mass spectrometry. The detection limits were 1 pg/1 when 250 ml of coastal water was preconcentrated. 

Pocurull et al. [130] used the online solid-phase extraction GCMS preconcentration method to determine organotin antifouling compounds in seawater 10 ng/1 detection limits were achieved using a 10 ml sample. 

Due to the predicted and previously detected low concentrations of pesticides in environmental samples (usually around the nanogram per liter level), a preconcentration step of the water samples is necessary prior to measurement. In this way, a preconcentration factor of several orders of magnitude (200-1,000-fold) is mandatory to reach the low detection limits necessary for the identification of pesticides, especially in complex wastewater samples. Also, the use of surrogate standards (e.g., triphenyl phosphate) added before the extraction step is a common practice in order to account for possible errors during the extraction process and for quantitative purposes. The commonly used extraction methods for polar compounds from water matrices involve isolation using liquid-liquid extraction (LLE) and solid-phase extraction (SPE), which are commented on below. Other methods such as semipermeable membrane devices (SPMD) are also mentioned. 

Preetha CR, Biju VM, Rao TP. On-line solid phase extraction preconcentration of ultratrace amounts of zinc in fractionated soil samples for determination by flow injection flame AAS. At. Spectrosc. 2003 24 118-124. 

In one study, however, atmospheric pressure chemical ionisation (APCI)-MS was applied for the simultaneous determination of LAS and octylphenol ethoxylates (OPEO) in surface waters after preconcentration by solid-phase extraction (SPE) on Cis cartridges [1]. In the chromatogram from a Ci-reversed phase (RP) column, peaks arising from both the anionic LAS and the non-ionic OPEO were detected after positive ionisation, while in negative ionisation mode, OPEO were discriminated and only the anionic surfactant was observed. Surprisingly, the relative sensitivity for detection of LAS was approximately five times higher in positive ion mode, which led the authors to the conclusion that this ionisation mode was desirable for quantitative work. 

Several strategies have been described for the preconcentration of sample components present at low concentrations. These techniques include zone sharpening,28-29 on-line packed columns,30 and transient capillary isotachophoresis (cITP).31-32 Other standard laboratory techniques are often used, including solid-phase extraction, protein precipitation, ultrafiltration, etc. Two important points to keep in mind when selecting a concentration protocol are the sample requirements of the method and the potential selectivity on relative concentrations of sample components. The latter point applies to purity and concentration analysis. 

Yu, C., Davey, M. H., Svec, F, and Frechet, J. M. (2001). Monolithic porous polymer for on-chip solid-phase extraction and preconcentration prepared by photoinitiated in situ polymerization within a microfluidic device. Anal. Chem. 73, 5088-5096. 

Retention of the analyte on a solid-phase extractant, followed by dissolution in a clean matrix (such as dilute nitric acid) to remove interferences and preconcentrate the analyte. 

E. Kenduezler, O. Yalcinkaya, S. Baytak and A. R. Tuerker, Application of full factorial design for the preconcentration of chromium by solid phase extraction with Amberlyst 36 resin, Microchim. Acta, 160(4), 2008, 389-395. 

Analytes can be separated from complex matrices by sample preparation techniques that include liquid extraction, supercritical fluid extraction, and solid-phase extraction. Dilute ionic analytes can be preconcentrated by adsorption onto an ion-exchange resin. Nonionic analytes can be concentrated by solid-phase extraction. Derivatization transforms the analyte into a more easily detected or separated form. 

High-performance LC determination is also compatible with the extraction of environmental water with an organic solvent such as methylene chloride or ethyl acetate (31,32) and solid-phase extraction (SPE) (33,34). Solid-phase extraction and liquid-liquid extraction (LLE) have been compared with respect to their ability to preconcentrate pesticides prior to HPLC analysis. The reproducibility of the method is better when C,8 cartridges are used than with conventional LLE, but LLE sometimes gives better recoveries, for example, for dimethoate, chlor-pyriphos ethyl, and carbofenothion (35). 

Pushing detection limits of nitroaromatic explosives into the parts per trillion (ppt) level requires sample preconcentration. Collins and coworkers used solid-phase extraction (SPE) of explosives from sea water which was followed by rapid on-chip separation and detection [18]. Explosives were eluted from SPE column by acetonitrile and were injected in the microchip separation channel. Lab-on-a-chip analysis was carried out in nonaqueous medium. The mixed acetonitrile/methanol separation buffer was used to produce the ionized red-colored products of TNT, TNB and tetryl [27,28]. The chemical reaction of the bases (hydroxide and methoxide anions) with trinitroaromatic explosives resulted in negatively charged products, which were readily separated by microchip... 

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