Solid phase extraction with cationic exchange

DMAE is extracted from simulants using solid phase extraction on a strong cation exchanger. The absorbed DMAE is removed from the absorbent with triethylamine and the resulting solution examined by GC using an internal standard... 

Cleanup of macrolides and lincosamides from coextracted material can also be accomplished with solid-phase extraction columns. Nonpolar sorbents such as XAD-2 resin (148) or reversed-phase sorbents (133, 134, 137, 141, 142) are usually employed in solid-phase extraction. In the latter case, ion-pairing with pentanesulfonic acid can also be applied for enhancing retention onto the hydro-phobic Ci8 material (154). However, these sorbents are not always effective for efficient cleanup of liver and kidney extracts. The basic character of macrolides and lincosamides suggests that cation-exchange sorbents such as aromatic-sulfonic acid (145,147), or polar sorbents such as silica (144,152,153), aminopropyl (139), or diol (149-151), can be powerful alternative approaches for isolation and/or cleanup of these compounds. 

Elimination of coextracted materials and concentration of tetracyclines have also been accomplished using mixed-phase extraction membranes with both re-versed-phase and cation-exchange properties (294,295), or solid-phase extraction columns packed with cation-exchange materials such as CM-Sephadex C-25 (301), aromatic sulfonic acid (310), and carboxylic acid (283, 300). For the same purpose, metal chelate affinity chromatography has also been employed. In this technique, the tetracyclines are specifically absorbed on the column sorbent by chelation with copper ions bound to small chelating Sepharose fast flow column (278-281, 294-296). 

After hydrolyzate acidification with hydrochloric acid at pH values lower than 1, quinoxaline-2-carboxylic acid is quantitatively extracted into ethyl acetate, chloroform, or dichloromethane, since at these strongly acidic conditions the ionization of their carboxylate moiety is suppressed (pK, 2.88), and then back-extracted into aqueous buffered solutions at pH 6.0 or higher. These liquid-liquid partitioning procedures isolate quinoxaline-2-carboxylic acid from a complex mixture of tissue hydrolysates, and provide an aqueous extract suitable for further purification by solid-phase extraction. This has been accomplished either with the strong cation-exchange resin AG MP-50 (419, 420) or with a polar silica column (422). 

A novel multiresidue method has been developed for quantitation of TBZ, the metabolite 5-hydroxythiabendazole (5-OH-TBZ) in raw cow s milk. The 5-HS04-TBZ was hydrolyzed quantitatively under acidic conditions to 5-OH-TBZ. The TBZ and 5-OH-TBZ were extracted from milk at pH 8.0 with ethyl acetate, followed by cleanup of the extract on a cation-exchange solid-phase extraction column. Analytes were separated with a cation-exchange stationary phase ... 

The method commonly proposed is based on cation-exchange extraction followed by derivatization of the fraction of interest with OPA (46,55,98,99,114,124-126) (when isolating BAs in wines). Solid-phase extraction has been performed with several stationary phases based on anionic (113) or cationic (37,39) exchangers or octadecylsilane groups (38), as well as a combination of both (51). 

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... 

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...

Sample purification and concentration used double-mechanism (cation exchange and reversed phase) solid phase extraction cartridges. The extracts from 5 mL of urine were dried, redissolved with 100 /aL of running buffer, and injected, to achieve a detection limit of 100 ng/mL. For peak identification, not only the retention times were used, but also the on-line-recorded UV spectra of the peaks, which were compared to computer-stored models. 

Desalting can be achieved by precipitation with ethanolic atmnonium acetate [4], solid-phase extraction (SPE), microdialysis [13], Fe " -loaded immobilized metal affinity chromatography (IMAC) [14], cation-exchange coluttms (SCX) [15-16], or combinations thereof [17-18]. The SCX procedure can be applied on-hne with direct infusion of the effluent into ESl-MS [15-16]. The mobile phase applied is similar to the one applied in LC-MS, i.e., 50% acetonitrile in 10 mmol/1 aqueous TEA. 

Reaction Blank of 0 NH2 and Peroxidase. Twenty five mg peroxidase, 100 pi of 0 NH2, and 3 ml of H2O2 were added sequentially to 100 ml of pH 6 phosphate buffer, and stirred for 6.5 hours. The reaction was then quenched by acidifying to pH 2 with acetic acid. The colored reaction products were sorbed onto a C18 solid phase extraction cartridge, rinsed with distilled deionized water, and then eluted with methanol. The methanol was removed using rotary evaporation and the reaction products redissolved in 2 ml of DMSO-d for NMR analysis. Reaction of Humic Acid with 0 nH2 in Presence of Bimessite. Four hundred mg of the soil humic acid was added to 200 ml of H2O and adjusted to pH 6 with IN NaOH. Two hundred pi of 0 NH2 and 50 mg of bimessite were added and the reaction mixture stirred for 6 days. The reaction solution was then dialyzed, filtered through a sintered glass funnel, H" - saturated on the cation exchange resin,... 

Logan, B. K., Stafford, D. T., Tebbett, I. R., and Moore, C. M. 1990. Rapid screening of 100 basic drugs and metabolites in urine using cation exchange solid-phase extraction and high-performance liquid chromatography with diode array detection, J. Anal. Toxicol., 14 154-159. 

Eiquid- or solid-phase extraction methods have been adopted for the isolation of catecholamines and their metabolites from urine samples. The liquid extraction system is ordinarily based on the formation of a complex, in alkaline medium, between diphenylborate and the diol group in the catecholamines. However, the liquid extraction methods reported in the literature are relatively tedious and often involved multiple extraction steps.For the more widely used solid-phase extraction methods, catecholamines may be selectively isolated from the urine sample by adsorption with activated alumina," " phenylboronic acid or cation-exchange resins. All the specimen preparative procedures are specific for the free catecholamines, i.e. the extracted catecholamines do not include the conjugated fraction. 

Cytokinins can also be purified effectively on solid phase extraction columns. Basic cytokinins in neutral buffer are not retained when applied to a SAX anion-exchange support but are absorbed when the eluting buffer is passed directly through a C,g cartridge from which they can be removed with 80% aqueous methanol [21,55]. When basic cytokinins are dissolved in 10 mM ammonium acetate buffer, pH 3.0, they are retained by a sex cation-exchange cartridge. The cartridge is then washed with the ammonium acetate buffer after which the cytokinins are eluted in 10% methanol in 2 M ammonium hydroxide [21]. This procedure provides a very effective purification of basic cytokinins in extracts from a variety of plant tissues. 

Several clean-up methods have incorporated the use of additional liquid-liquid steps with solvents such as chloroform and ethyl acetate. Alternatively, some authors have turned to ultrafiltration for further purification.Additionally, hexane is extensively used in several methods to further remove non-polar matrix components such as fats and lipids. By far, the most popular clean-up technique reported in the literature is the use of solid phase extraction (SPE). Some common phases reported include CIS cartridges such as SepPak C18, Strata Chromobond C18, " and Mega Bond Elut C18. The use of silica, alumina, and Extralut " " has also been reported, as well as polymeric cartridges such as Oasis HLB. The latter phase has been reported as the basis of an on-line clean-up procedure. Because of their amphoteric nature, as both weak acids and weak bases, the sulfonamides also lend themselves to analysis by ion exchange. Cationic SPE has been reported by several authors.On the basis of the same principles, anionic exchange has also been used. " ... 

Solid-phase extraction using co-polymeric bonded phases with hydrophobic and cation exchanged functionalities has also been used for the extraction of heroin and metabolites from biological fluids and tissues. Solid-phase extraction can yield clean extracts with efficient recovery of analytes. In... 

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