Hydrophobicity solid-phase extraction

Brockman, A. H., Shah, N. N., and Orlando, R., Optimization of a hydrophobic solid-phase extraction interface for matrix-assisted laser desorption/ionization, yoMmaZo/MassS/recfronrefry, 33,1141-1147, 1998. 

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. 

Recently, solid phase extraction (SPE) has been used to isolate members of this class of compounds. No solid phase support has been used exclusively and both hydrophobic- and hydrophilic-based solid phase extraction columns have been used for this assay. 

More elaborate sample preparation is often needed for complex sample matrices, e.g., lotions and creams. Many newer SP technologies such as solid-phase extraction (SPE), supercritical fluid extraction (SFE), pressurized fluid extraction, accelerated solvent extraction (ASE), and robotics are frequently utilized (see Ref. [2]). Dosage forms such as suppositories, lotions, or creams containing a preponderance of hydrophobic matrices might require more elaborate SP and sample cleanup, such as SPE or liquid-liquid extraction. 

Agonists are particularly suited to reversed-phase solid-phase extraction due, in part, to their relatively nonpolar aliphatic moiety, which can interact with the hydrophobic octadecyl- and octyl-based sorbents of the cartridge (472, 473, 475, 480,486, 487). By adjusting the pH of the sample extracts at values greater than 10, optimum retention of the analytes can be achieved. Adsorption solid-phase extraction using a neutral alumina sorbent has also been described for improved cleanup of liver homogenates (482). 

As mentioned above, most MIPs are synthesized in organic solvents to preserve the hydrogen and electrostatic interactions between template and monomer. However, for the application to solid-phase extraction (SPE) where the target is most of the time in water samples or in biological fluids, a lot of studies have been carried out to examine the influence of binding media parameters (solvent polarity and composition, buffer pH, concentration, ionic strength, etc.) with the aim of attenuating non-specific adsorption of the analyte due to hydrophobic interactions which predominate in such media. For a recent review, see Tse Sum Bui and Haupt [95]. 

The selection of adsorbent packing material is based on the polarity of pollutants to be analyzed. The nonpolar hydrophobic adsorbents retain the nonpolar analytes and allow the polar substances to pass through the column. The hydrophilic adsorbents adsorb the polar components, allowing the nonpolar materials to pass through. Various stationary phases for solid phase extraction are listed below in Table 1.5.1. 

A monolithic hydrophobic polymer formed by photoinitiated polymerization for on-chip solid-phase extraction is shown in Figure 5.6. The polymer mixture includes butyl methacrylate (BMA) and ethylene dimethacrylate (EDMA), with the pore size controlled by the composition of the hexane/methanol porogenic mixture. The degree of pre-concentration depends on the flow rate, as shown in the pre-concentration of GFP at three flow rates (see Figure 5.7). The factors of pre-concentration were 355, 756, and 1002 for the flow rates of 3, 1.03, and 0.53 rE/min, respectively [342]. 

Initially, vidarabine was used as the internal standard for penciclovir in a method based on mixed-mode strong cation exchange (MCX) solid-phase extraction due to their similar properties, particularly hydrophobicity (Fig. 14a). Quite stable IS responses were obtained in a run consisted mainly of CS and QC samples with a CV of 13.02 % (Fig. 14b). However, 43 % of the CS and QC samples did not meet the acceptance criterion of accuracy. On the other hand, when penciclovir-d4 was used as the internal standard, all the CS and QC samples met the acceptance criterion in accuracy though the IS responses were more variable (the CV in IS responses was 23.81 %, Fig. 14c). 

Fig. 14 (a, top) Hydrophobicity (log D) vs. pH curves for penciclovir and vidarabine. (b, middle) Less internal standard response variation was observed while using vidarabine as the internal standard (CV= 13.02 %) but 43 % of the calibration standards (CS) and quality controls (QC) were rejected. Extraction MCX (mixed-mode strong cation exchange)-based solid-phase extraction, (c, bottom) More IS response variation was observed while using a deuterated internal standard, penciclovir-d4 (CV = 23.81 %) but 100 % of the CS and QC samples were accepted. Reproduced from ref. [36] with permission from Elsevier... 

Freidig, A.P., Garciano, E.A., Busser, F.J.M., and Hermens, J.L.P. (1998) Estimating impact of humic acid on bioavailability and bioaccumulation of hydrophobic chemical in guppies using kinetic solid-phase extraction. Environ. Toxicol. Chem. 17, 998-1004. 

Just as the interiors of micelles in water provide a hydrophobic environment to solubilize chlorobiphenyls and then photodegrade them by reductive dechlorination, so do octadecyl-functionalized silica gel [89], normally used as reverse phase packing in HPLC and for solid-phase extraction, and the hquid-semisohd polydimethylsiloxane [-OSi(CH3)2 -] [90,91], also used for solid-phase extraction. In both media, reductive dechlorination is the primary photochemical pathway. 

Liu,Z. Kang, X. Fang, F. 2010. Solid phase extraction with electrospun nanofibers for determination ofretinolandalpha-tocopherolinplasma.Microchim. Acta. 168 59-64. Mac-Mod., 2011. Mac-Mod Analytical, ProtoSlL C30 reversed phase HPLC columns for the separation of hydrophobic structural isomers, from http //www. bischoff-chrom.com/pdf/BlSCHOFF-Appl-l%20%5BSchreibgesch%FCtzt%5D. pdf. accessed March 26, 2011. 

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