Solid normal-phase extraction

The first bioanalytical application of LC-GC was presented by Grob et al. (119). These authors proposed this coupled system for the determination of diethylstilbe-strol in urine as a replacement for GC-MS. After hydrolysis, clean-up by solid-phase extraction and derivatization by pentafluorobenzyl bromide, the extract was separated with normal-phase LC by using cyclohexane/1 % tetrahydrofuran (THE) at a flow-rate of 260 p.l/min as the mobile phase. The result of LC-UV analysis of a urine sample and GC with electron-capture detection (ECD) of the LC fraction are shown in Ligures 11.8(a) and (b), respectively. The practical detection limits varied between about 0.1 and 0.3 ppb, depending on the urine being analysed. By use of... 

Water solubility, dissociation constant(s) and n-octanol/water partition coefficients allow one to predict how an analyte may behave on normal-phase (NP), reversed-phase (RP), or ion-exchange solid-phase extraction (SPE) for sample enrichment and cleanup. 

Although SPE can be done in a batch equilibration similar to that used in LLE, it is much more common to use a small tube (minicolumn) or cartridge packed with the solid particles. SPE is often referred to as LSE, bonded phase or sorbent extraction SPE is a refinement of open-column chromatography. The mechanisms of retention include reversed phase, normal phase, and ion exchange. 

Liquid chromatographic clean up [441,443,450] has been used either in normal phase flow using alumina, silica, or florisil [22,189,403,481,484] or with reverse-phase (RP) columns [409,452,480]. In most cases these techniques are well established and are used in an off-line mode, primarily to remove the bulk of co-extracted materials prior to a more refined clean-up prior to the final determination. These columns may be prepared in the laboratory [22,403 -405] or commercial solid phase extraction (SPE) cartridges can be used [409,452, 463,470,485,486]. In both cases, the normal phase cartridges and column materials are disposable since many of the polar co-extractants bind firmly to the substrate surface and are difficult to remove. This has been overcome to some... 

Gustavson et al. (2000) developed a convenient and novel solid phase extraction (SPE) method for the removal of methyl oleate from SPMD dialysates containing PAHs. A small SPE column (1 g or 0.5 g) containing a dual-zone silica (normal phase)-based restricted-access sorbent (Diazem, Midland, MI, USA) is used for the separation. The capacity of this sorbent to remove methyl oleate is about 1.8% (lipid/sorbent wt wt ). The PAHs are eluted with 19 mL of hexane and methylene chloride (97 3 VV ) and recoveries of all PAHs are typically >72%. 

Prior to analysis of -lactam residues in liquid foods such as milk, a pretreatment step for fat removal, accomplished by centrifugation (69-71), is usually required. In instances where milk is to be submitted to ultrafiltration, dilution with water/acetonitrile (72-76) or water/acetonitrile/methanol (77-79) is often needed. Milk filtration (80) or dilution with acetate (81, 82) or phosphate buffers (83) is sometimes essential prior to solid-phase extraction. Unlike milk, semisolid food samples such as muscle, kidney, and liver require normally more intensive sample pretreatment. Tissue break-up is mostly carried out by the combined use of a mincing apparatus and a tissue homogenizer. 

Cleanup by solid-phase extraction has also been widely employed since it is a simple, fairly inexpensive, and easy-to-perform procedure for purification of the crude extract. The use of disposable solid-phase extraction columns is currently part of most, if not all, modern analytical methods for the determination of anthelminthics in biological matrices at residue levels. Both normal-phase columns based on silica (333-335, 340, 367, 372), alumina (346, 373-375), or aminopropyl (339, 365, 370) materials, and reversed-phase columns based on Ci8 (319, 323, 324, 328, 344, 346, 347, 349-351, 357-359, 364, 367) and cyclohexyl (329, 332, 360) sorbents have been described in analytical applications. 

In some instances, combinations of normal- and reversed-phase columns can also be used for better purification of the crude extract. Combinations of Ci8 and alumina or Cig and silica solid-phase extraction columns have been successfully employed in the analysis of ivermectin residues in animal tissues (346) and bovine plasma (348), respectively. Elimination of coextracted materials and concentration of the analytes has also been accomplished using mixed-phase extraction columns. Such a copolymeric bonded silica column with both hydro-phobic and cationic functions has been employed in the analysis of hygromycin B in plasma, serum and milk (326). 

Fig. 19 Randomly scattered low internal standard (IS) responses observed for incurred samples only, whose IS responses were within normal range during repeat analyses. Analyte olanzapine IS olanzapine-d3 sample pretreatment at clinic 25 % (w/v) L-ascorbic add added to plasma in a ratio of 1.25 100 (v/v) extraction MCX (mixed-mode strong cation exchange)-based solid-phase extraction. An incurred sample was coded for reassay when its IS response was outside 50 % of the mean IS response of the accepted calibration standards and quality controls. Reproduced from ref. [36] with permission from Elsevier...

Separation and purification of three turmerones, e.g. ar-turmerone, a- and P-turmerone, from turmeric oil extracted by supercritical carbon dioxide gave 71% purify by weight. Subsequently, purification using a normal-phase silica gel 60 column could separate and purify three major turmerones with 86% purify by weight of ar-turmerone and 81% purity by weight of a- and P-turmerone. These were identified by liquid-solid chromatography, NMR qualification and HPLC quantification, respectively (Li-Hsun Chang et al., 2006). 

T. Hirai, Usability of a normal solid-phase extraction as the sample clean-up procedure for urinary drug analysis by high-performance liquid chromatography, CCAB 97 Mini Review, http //neo.pharm.hiroshima-u.ac.jp/ccab/lst/mini review/mr002 /hirai.html (August 1, 2002). 

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. 

CuUere, L., Aznar, M., Cacho, J., and Eerreira, V. (2003). Fast fractionation of complex organic extracts by normal-phase chromatography on a solid-phase extraction polymeric sorbent -Optimization of a method to fractionate wine flavor extracts. J. Chromatogr. A., 1017, 17-26. 

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