Bonded-phase silica cartridges

In summary, the development of materials for the extraction of pesticides from water samples has progressed from simple liquid-liquid extraction for the principal active compound to sophisticated SPE media capable of exclusively trapping the target pesticide and metabolites selectively. The development of alkyl bonded phase silica cartridges and extraction disks combined with on-line extraction techniques is currently the principal means used for the extraction and trace enrichment of pesticides and metabolites from water. 

An SPE method has been developed to replace the classical LLP method. Water sample is extracted with an SPE column such as Cig and styrene-divinylbenzene copolymer (PS-2) cartridges, which consist of a reversed bonded-phase silica sorbent, provided as an extraction tool. This is a simple and rapid method, and applied to the determination of residual amounts of naproanilide, propanil, mefenacet, etc. This system determines the residual amounts of most of the pesticides and has been successfully applied to determination of pesticides in water. 

Bonded-phase silica and ion-exchange resins in plastic cartridges and mini-columns are very useful for off-line prepurification of samples, especially those for preparative chromatography, when appropriate pre- or guard columns may not be available for on-line clean-up of a sample. 

Junk, G. A., Avery, M. J., and Richard, J. J. 1988. Interferences in solid-phase extraction using C-18 bonded porous silica cartridges, Anal. Chem.,6W. 1347-1350. 

Some authors have considered the MLC approach still interesting for the determination of drugs in physiological fluids, when a previous separation step is required. It is expected that the combined selectivity of extraction procedures and MLC will provide wide resolution power to avoid presumable restrictions. Thus, the antipyrine metabolites 4-aminoantipyrine, 4-methylaminoantipyrine and 4-formylaminoantipyrine were well separated in plasma samples and eluted in less than 5 min with a 0.1 M-2.5% 1-pentanol mobile phase and C18 column. Extraction widi methylene chloride [27], or through disposable C18 bonded porous silica cartridges [28], with methanol as an eluent, were necessary to remove the metabolites from the... 

The alternative technique for analyzing 1,4-dioxane is HPLC. Scalia proposed a method by solid-phase extraction using octadecyl-bonded silica cartridges and analyzed directly on a reverse phase column with UV detection at 200 nm and acetonitrile-water as eluent [328-330]. 

Application of SPE to sample clean-up started in 1977 with the introduction of disposable cartridges packed with silica-based bonded phase sorbents. The solid phase extraction term was devised in 1982. The most commonly cited advantages of SPE over liquid-liquid extraction (LLE) as practiced on a macroscale include the reduced time and labor requirements, use of much lower volumes of solvents, minimal risk of emulsion formation, selectivity achievable when desired, wide choices of sorbents, and amenability to automation. The principle of operation consists of four steps (1) conditioning of the sorbent with a solvent and water or buffer, (2) loading of the sample in an aqueous or aqueous low organic medium, (3) washing away unwanted components with a suitable combination of solvents, and (4) elution of the desired compound with an appropriate organic solvent. 

Imazalil, OPP, and TBZ residues were determined using an HPLC system, consisting of a ternary HPLC pump attached to 250 X 4.6-mm-ID Hichrom RPB 5-/tm column with a 10 X 3.2-mm-ID guard cartridge column. The packing material of both columns was base-deactivated silica, fully endcapped with a bonded phase of Cg/C]8. The mobile phase was methanol/water at a flow rate of 1 ml/min at ambient temperature. Imazalil in the eluate was detected with UV detector at 204 nm a fluorescence detector was used to monitor OPP (excitation 285 nm, emission 350 nm) and TBZ (excitation 296 nm, emission 350 nm) (47). 

With normal-phase HPLC, oil samples were analyzed as is by simple dilution in n-hexane. A Du Pont Zorbax amino-bonded phase column, 25 cm x 0.46 cm ID, was used, with n-hexane and dichloromethane as solvents. For reversed-phase HPLC, Vydac 201TP5 columns were used (25 cm x 0.46 cm ID for analytical scale and 25 cm x 1 cm ID for preparative scale). Samples for reversed-phase HPLC were fractionated in order to remove the saturated hydrocarbons which can interfere with the separation mechanism. The samples dissolved in n-hexane were passed Baker silica solid-phase extraction cartridges. The PAH fraction was then collected by eluting with a 1 1 mixture of dichloromethane and methanol. Acetonitrile and dichloromethane were used in the HPLC gradient. 

A comparison study of Cig-bonded silica cartridges and polystyrene-divinylbenzene copolymer membrane absorption disks showed that the latter were the more effective for SPE of phenols at the 0.5 ppb concentration levels (70-98% recoveries), whereas the Cis cartridges were preferable for higher concentration levels (10 ppb) because smaller sample and solvent volumes were required and analysis time was therefore shorter. End analysis was by LC-ELD, with a phosphate buffer-acetonitrile-methanol mixture as mobile phase and coulometric detection at +750 mV. A study was carried on the preconcentration step of phenol, < -, m-, p-methylphenol, < -, m-, p-chlorophenol, 2,5-, 2,6-dichlorophenol, catechol (42), resorcinol (20) etc., at 0.5 and 5 figL concentrations. SPE utilizing a divinylbenzene-hydrophilic methacrylate copolymer gel showed recoveries better than... 

However, in order for the cation-exchange mechanism to work on atrazine, the pH of the sample must be lower than the pAT, of the analyte. This would require lowering the pH of the sample to 1.0, and a substantial amount of acid is required for this process. Furthermore, acidification to this low of a pH will protonate the organic acids naturally present in the water sample and increase the possibility of interferences when the sample is eluted from the SPE sorbent. Furthermore, the bonded-phase ion-exchange SPE cartridges are not capable of operating at this low of pH because of dissolution of the silica matrix, although it would be possible to use a polymeric sorbent. 

Setchell, K. D. R., and Worthington, J., A rapid method for the quantitative extraction of bile acids and their conjugates from serum using commercially available reverse-phase octadecylsilane bonded silica cartridges. Clin. Chim. Acta 125, 135-144 (1982). 

A 50-g ground tissue sample was homogenized twice with 100 mL of methanol. The homogenates were centrifuged and the two supernatants combined. A 10 mL aliquot of the extract was diluted with 2 mL of water, the methanol evaporated, and an additional 5 mL of water added. The aqueous sample was adjusted to pH 10.5 with 100 iL of 2 M sodium bicarbonate and extracted twice with 10 mL of ethyl acetate. The ethyl acetate was evaporated to dryness, the residue dissolved in 5 mL of acetonitrile/methanol (9 1), and applied to a Bond Elut acid washed silica cartridge (Analytichem International, Harbor City, CA). After washing the cartridge with small amounts of acetonitrile/methanol (9 1), methanol, and dichloromethane, die ractopamine HCl was eluted with 8 mL of dichloromethane/methanol/triethylamine (84 15 1). The eluate was evaporated to dryness in a rotary vacuum evaporator, the residue dissolved in 2 mL of the HPLC mobile phase, and analyzed by HPLC. 

Chemically bonded reversed-phase silicas Cig and to a lesser extent Cg sUica cartridges are packed with the same stationary phases as in LC columns, but with a larger particle size." " Although Cig sorbent with high carbon loading and some residual silanol are best suited, they are not able to extract polar compounds from large sample volumes. Therefore Cig silica is rarely used for multrresidue environmental analyses. 

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