Organic acids solid phase extraction

Prepai ative isolation of nonvolatile and semivolatile organic compounds fractions (hydrophobic weak acids, hydrophobic weak bases, hydrophobic neutrals, humic and fulvic acids) from natural and drinking waters in optimal conditions was systematically investigated by solid-phase extraction method with porous polymer sorbents followed by isolation from general concentrate of antropogenic and/or toxic semivolatile compounds produced in chlorination and ozonation processes. 

Cherchi, A., Spanedda, L., Tuberoso, C., and Cabras, P. (1994). Solid phase extraction and high-performance liquid chromatographic determination of organic acids in honey. 

Sum-ez-Luque, S., Mato, I., Huidobro, J. F., and Simal-Lozano, J. (2002b). Solid-phase extraction procedure to remove organic acids from honey. /. Chromatogr. B 770, 77-82. 

Exudate collection in trap solutions usually requires subsequent concentration steps (vacuum evaporation, lyophilization) due to the low concentration of exudate compounds. Depending on the composition of the trap solution, the reduction of sample volume can lead to high salt concentrations, which may interfere with subsequent analysis or may even cause irreversible precipitation of certain exudate compounds (e.g., Ca-citrate, Ca-oxalate, proteins). Therefore, if possible, removal of interfering salts by use of ion exchange resins prior to sample concentration is recommended. Alternatively, solid-phase extraction techniques may be employed for enrichment of exudate compounds from the diluted trap solution (11,22). High-molecular-weight compounds may be concentrated by precipitation with organic solvents [methanol, ethanol, acetone 80% (v/v) for polysaccharides and proteins] or acidification [trichloroacetic acid 10% (w/v), per-... 

Kuklenyik Z., Needham L.L., and Calafat A.M., 2005. Measurement of 18 perfluorinated organic acids and amides in human serum using online solid-phase extraction. Anal Chem 77 6085. 

When liquid samples such as serum, plasma, milk, or honey are not to be extracted using direct liquid-liquid partitions with organic solvents but through use of solid-phase extraction or matrix solid-phase dispersion techniques, dilution with water (323, 324), phosphate buffer saline (325), or phosphoric acid (326, 327) is often the only sample preparation procedure applied. Milk analysis sometimes requires further pretreatment for fat removal (328). Centrifugation at about 7000g at 4-10 C for 20 min is the usually applied procedure for making the fat floating on top of milk readily eliminated. 

D.L. Ambrose, J.S. Fritz, M.R. Buchmeiser, N. Atzl, and G.K. Bonn, New, high-capacity carboxylic acid functionalized resins for solid-phase extraction of a broad range of organic compounds,/. Chromatogr. A, 786(2) 259-268, October 1997. 

Methods involve extractions of analytes into organic solvents, as well as treatments with acidic or basic reagents. Solid-phase extraction can be used for removal and pre-concentrations of analytes in aqueous solutions. Applications of low-power focused microwave technology have been investigated as a means of dissolution, and good results have been reported for extractions of organometal-lic compounds of tin and mercury (Schmitt et al., 1996 Szpunar et al., 1996). Analyses of CRMs were used for verification. The time necessary for quantitative isolations of the analytes was greatly reduced, e.g. 24 h to 5 min. In addition, there were reductions in solvent volumes, and improvement in analyte recoveries. Some of the analytical procedures for speciation of particular elements such as mercury, described later in this chapter, include microwave-assisted sample preparation. 

For sample preparation, protein precipitation or liq-uid/liquid extraction can also be applied instead of solid phase extraction. Gluth et al. (1988) described for a toxicokinetic assay for Sotalol a threefold combination of these principles. A protein precipitation using 5 M perchloric acid was followed by a liquid/liquid extraction into a mixture of n-pentanol-chloroform 1/3 at pH 9. Thereafter, the organic phase was transferred to another glass tube and the analyte back extracted into 0.05 M sulfuric acid. 

Liquid-liquid extraction (LLE), solid phase extraction (SPE), and solid phase micro-extraction (SPME) are frequently applied for sample pretreatment. The type of extraction is highly related to the type of metabolites selected for determination. In previous metabolomics studies, extraction was focused on compounds of adequate stability that could be extracted together (carbohydrates, esters, amino acids, or organic acids). 

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