Sample extraction and preconcentration

There are several future trends for the development of passive sampling techniques. The first is the development of devices that can be used to monitor emerging environmental pollutants. Recently, attention has shifted from hydrophobic persistent organic pollutants to compounds with a medium-to-high polarity, for example, polar pesticides, pharmaceuticals, and personal care products.82 147148 Novel materials will need to be tested as selective receiving phases (e.g., ionic liquids, molecularly imprinted polymers, and immunoadsorbents), together with membrane materials that permit the selective diffusion of these chemicals. The sample extraction and preconcentration methods used for these devices will need to be compatible with LC-MS analytical techniques. 

Liquid-liquid extraction (LLE) is among the oldest sample extraction and preconcentration techniques available in analytical chemistry. LLE is a method whereby two immiscible phases, generahy an organic solvent and an aqueous solution, are brought into contact in order to extract one or more analytes from one phase into the other. If the receiving phase has a smaller volume than the donor phase, preconcentration can be effected. The separation mechanism is, like SPE, based on partitioning. At equilibrium, the partition coefficient of analyte i (Ki) in a two-phase system is given by... 

Analytical Applications of IL-Based Surfactants in Sample Extraction and Preconcentration... 

Most existing methods are based on instrumental analysis involving exhaustive sample pretreatment and preconcentration steps, followed by purification and fractionation before final chromatographic separation and detection. For fat and oil samples, dissolving the lipids in an appropriate solvent is usually the first treatment. This has been achieved by melting the fat at 90°C followed by LLE or direct solid liquid extraction (SEE) with an apolar solvent [37], column extraction with a mixture of apolar solvents after drying of the sample with anhydrous Na2S04, Soxhlet extraction and/or sonication with apolar solvents. Typically, sample intake is between 0.5 g and 1 g and quantitative recoveries >60% have been reported. 

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... 

Audunsson, G. 1986. Aqueous/aqueous extraction by means of a liquid membrane for sample cleanup and preconcentration of amines in a flow system. Anal. Chem. 58 2714—2723. 

Lezamiz, J. and J.A. Jonsson. 2007. Development of a simple hollow fibre supported liquid membrane extraction method to extract and preconcentrate dinitrophenols in environmental samples at ng L-1 level by liquid chromatography. J. Chromatogr. A 1152 226-233. 

Ma, M. and F.L. Cantwell. 1999. Solvent microextraction with simultaneous back-extraction for sample cleanup and preconcentration Preconcentration into a single microdrop. Anal. Chem. 71 388-393. 

The techniques of sample preparation, extraction (isolation), and/or preconcentration of analytes are usually applied in the analysis of trace components of gaseous, liquid, and solid samples. During this operation, transport of analytes from primary matrices (donors) to the secondary matrix (the acceptor) takes place. It should be remembered, however, that the extraction and preconcentration steps could be a source of environmental pollution. The techniques of sample preparation introduced in this chapter have the following advantages253 ... 

Padron Sanz, C., Z. Sosa Ferrera, and J.J. Santana Rodriguez. 2002. Extraction and preconcentration of polychlorinated dibenzo-p-dioxins using the cloud-point methodology. Application to their determination in water samples by high-performance liquid chromatography. Anal. Chim. Acta 470 205-214. 

Bruland and Franks [15] investigated the determination of Cu, Cd, Zn and Ni in seawater by graphite-furnace atomic absorption spectrometry, carrying out a strict comparison of sampling techniques and preconcentration techniques (solvent extraction and chelating resin methods) [15]. 

The following are steps to be followed for sample preparation and preconcentration in the case of aqueous samples. If other radionuclides (Pu, Am, and Sr), are also analyzed in the same sample, the MnOj preconcentration steps are generally performed first to remove the transuranics, followed by Cs extraction with AMP and then, the Sr fraction is removed last as the oxalate. 

Cukrowska E, Chimuka L, Nsengimana H, and Kwaramba V. Application of supported liquid membrane probe for extraction and preconcentration of organotin compounds from environmental water samples. Anal. Chim. Acta 2004 523 141-147. 

S. Motomizu, T. Sakai, On-line sample pretreatment extraction and preconcentration, in S.D. Kolev, I.D. McKelvie (Eds.), Advances in Flow Injection Analysis and Related Techniques, Wilson and Wilson s Comprehensive Analytical Chemistry, vol. 54, Elsevier, Amsterdam, 2008, pp. 159—201. Chapter 7. 

Until recently, samples for FIA were already extracted. Altered, centrifuged or pretreated in some way prior to assay. However, some sample preparation and preconcentration steps can now be accommodated in FIA. Some examples are on-line liquid-liquid extraction, solid phase extraction and ion-exchange procedures. In this way, FIA is managing to convert some traditionally labour-intensive steps into automated operations that have higher precision and faster throughput. FIA can also tolerate other sample types, such as fermentation broth samples and even gases through the use of silicon membrane separators and gas diffusion systems, respectively. 

SPE is currently the most common method in use for the extraction and preconcentration of PAHs from water samples and is the process of selectively removing an analyte from the solution phase through physical or chemical attractive forces into or onto a solid phase. For most nonpolar to... 

Merino, F., Rubio, S., and Perez-Benito, D., Acid-induced cloud point extraction and preconcentration of polycyclic aromatic hydrocarbons from environmental solid samples, J. Chromatogr. A, 962, 1-8, 2002. 

Generally, only the sampling operations are performed in the field and other operations are performed in the laboratory. However, when the PCB concentrations are so low that large amounts of sample have to be collected, the extraction and preconcentration of analytes can be performed in the held in order to facilitate the storage and transport in the laboratory. 

Since its introduction, SPME has found numerous applicahons in the analysis of different classes of compounds present in various matrices. Several analytical methods for the determination of OCPs in water samples which make use of SPME as extracting and preconcentrating technique have been described. Magdic and Pawliszyn analyzed environmental water samples for the determination of OCPs using a PDMS-coated hber (him thickness 100 /rm). PDMS was preferred to other commercially available coating, i.e., polyacrylate, the latter being... 

SPME was hrst used by Pawliszyn et al. in 1990. It is a two-step process conductive to the simultaneous extraction and preconcentration of analytes form sample matrices. In the first step, a fused-silica fiber coated with a polymeric stationary phase is exposed to the sample matrix where the analyte partitions between the matrix and the polymeric stationary phase. In the second step, the fiber/analyte is transferred to the analytical instrument for desorption, separation, and quantification. SPME has a number of advantages over traditional extraction techniques for pesticides. In fact, it is fast, simple, solvent-free, and easily automated for both GC and HPLC instruments. It exhibits good linearity and sensitivity. Thus, carbamate and organophosphorus pesticides in golf course samples were successfully extracted by SPME and analyzed by HPLC by Jinno et al. ... 

G. Audunsson, Aqueous/Aqueous Extraction by Means of a Liquid Membrane for Sample Cleanup and Preconcentration of Amines in a Flow System. Anal. Chem., 58 (1986) 2714. 

Solid phase extraction procedures are now commonplace as a means of sample cleanup and preconcentration in chromatography. Espinosa et al. (1999) used strong anion exchange (SAX) solid phase cartridges to concentrate and isolate phosphorus-... 

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