Filtration solid-phase extraction

The CUSAL-HPLC couple has been combined additionally with pre- or post-column derivatization. Thus, pre-column derivatization was used for the determination of colistin A and B in feeds following USAL, the analytes were derivatized with o-phthaldialdehyde/2-mercaptoethanol and separated by HPLC for fluorimetric detection [48]. The experimental set-up used is depicted in Fig. 4.1 OA. Another application of CUSAL-HPLC is the determination of A/-methylcarbamates in soils and food [49] (see Fig. 4.10B), where the analytes were also derivatized with o-phthaldialdehyde after separation for fluorescence-based monitoring. A number of steps of the process including leaching, filtration, solid-phase extraction, liquid chromatographic separation, post-column derivatization and fluorescence detection were performed on-line, all in an automated manner. 

A. Caballo-Lopez, M.D. Luque de Castro, Continuous ultrasound-assisted extraction coupled to on line filtration—solid-phase extraction—column liquid chromatography—post column derivatisation—fluorescence detection for the determination of N-methylcarbamates in soil and food, J. Chromatogr. A 998 (2003) 51. 

For the purification of compounds, methods including molecular filtration, solid phase extraction (SPE, SPME), solvent extraction, and a variety of basic chromatographic techniques (thin layer, low pressure, ion exchange, size exclusion, etc.), HPLC, and GC (with derivatization of nonvolatile compounds) can be used. Additionally, instrumentation to identify compounds is available, such as the different spectrometric applications, including infrared (IR), mass (MS), ultraviolet and visible (UV-Vis), and NMR spectroscopy. In recent years, the so-called hyphenated techniques (combined chromatographic and spectral methods such as... 

Chlorophenoxy acids Soil (postcolumn) HPLC/intrinsic properties UV-spectrophotometry 10-50 mg I extraction/inline filtration/solid-phase extraction Continuous subcritical water... 

W whole (unfiltered) water sample P particulate phase D dissolved + colloidal phase. LLE liquid - liquid extraction F - SPE filtration - solid phase extraction F filtration GC-MS gas chromatography - mass spectrometry GC - FH) gas chromatography - flame ionization detection HPLC - FI high perfomance liquid chromatograph - fluorescence spectrophotometry C18 - FI Cl8 column chromatography - fluorescence spectrophotometry. 

Two approaches have been used to separate the analyte from its matrix in particulate gravimetry. The most common approach is filtration, in which solid particulates are separated from their gas, liquid, or solid matrix. A second approach uses a liquid-phase or solid-phase extraction. 

This sample preparation involved, firstly, an extraction and the elimination of the solid matrix by filtration and, secondly, a concentration procedure employing a solid phase extraction cartridge. The compounds of interest were separated solely by dispersive interactions with the reversed phase. In the example given, the corn meal was spiked with the aflatoxins. 

GC, utilizing flame ionization detection (FID), has been used to measure diisopropyl methylphosphonate in meat, grain, or milk (Caton et al. 1994). Sample preparation steps include homogenization, filtration, dialysis, and extraction on a solid sorbent. Two common solid phase extractants, Tenax GC and octadecylsilane bonded silica gel (C18 Silica), were compared by Caton et al. (1994). They reported 70% recovery when using Tenax GC and 85% recovery when using C18 Silica. Sensitivity was not reported. Equilibrium experiments indicate that 8-10 mg of Tenax GC are required to achieve maximum recovery of each g of diisopropyl methylphosphonate (Caton et al. 1994). By extrapolating these... 

Supported scavengers are reactive species that selectively quench and/or sequester by-products of the reaction or remove any excess starting materials, and are subsequently removed by filtration (Fig. 2.2). These species, which allow hquid-solid phase extraction are also often referred to as sequestering agents or quenching agents . 

However, the solution obtained after denaturation might include, depending on the application, other components besides the liberated marker ( matrix ). If a small amount of target material is used in the binding assay, the quantity of remaining matrix will be so low that it hardly disturbs the quantitation and the sample can be measured directly by LC-MS without further sample preparation (e.g. membrane filtration or solid phase extraction [78]). 

Jenkins et al. developed a capillary electrophoresis system for the measurement of iohexol as a marker of the glomerular filtration rate (GFR) with a run time of 5.25 min and a coefficient of variation (CV) of 4.3% at 80 mg L" [121]. The GFR, calculated from the plasma clearance, had a reproducibility of 5.47 %. A similar approach (liquid chromatography-mass spectrometry with positive electrospray ionization after enrichment by solid phase extraction) was applied by Putschew et al. for the determination of iodinated contrast agents in treatment plant effluents and surface waters [118]. 

As well as typical sample preparation methods such as filtration and liquid-liquid extraction, newer developments are now extensively used. The first of these is solid-phase extraction (SPE). This is a rapid, economical, and sensitive technique that uses several different types of cartridges and disks, with a variety of sorbents. Sample preparation and concentration can be achieved in a single step. Interfering sugars can be eluted with aqueous methanol on reversed-phase columns prior to elution of flavonoids with methanol. 

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. 

This method is used to simplify a chromatogram by reducing the number of compounds in a sample to the six aglycons. This protocol describes the dilution, preparation (including solid phase extraction and acid hydrolysis), filtration, and reversed-phase HPLC analysis of the sample. 

Besides solid-phase extraction, column chromatography is also often used for cleanup and purification of polyphenolics from plant material. Ionic adsorbants (polyvinylpyrrolidone or PVP, polyamides, and Sephadex LH-20) and Amberlite XAD-2 resin have been used to isolate and purify polyphenolics from crude extracts. For the separation of polyphenolics from plant material, column chromatography using Sephadex LH-20, a gel-filtration matrix, is often used with various eluting solvents (Park and Lee, 1996). The most widely used solvents for column chromatography are aqueous methanol and aqueous ethanol. 

This fractionation step may be optional. Some samples can be directly analyzed by HPLC after filtration (step 2) without solid-phase extraction. Anthocyanins that can be detected at 280 nm can interfere with the separation of some polyphenolics. If the analyst is interested in nonanthocyanin polyphenolics, and especially if plant materials containing high levels of anthocyanins are being analyzed, this fractionation technique should be utilized. 

Indyk and Woollard (195) demonstrated that the removal of cholesterol from the un-saponifiable fraction of vitamin D-supplemented whole milk powder by methanolic precipitation and filtration was an adequate cleanup procedure, making semipreparative HPLC unnecessary. This simplified procedure was made possible by connecting two analytical columns in series. The tandem columns adequately separated vitamins D2 and D3 from one another and from vitamins A and E. The analysis of infant formulas (100) required cleanup by silica solid-phase extraction to remove the minor tocopherols and tocotrienols, which constituted potential sources of interference. 

H-Lys(Fmoc)-Pro-Gly-Lys[Z(N02)]-Glu(OtBu)-Lys(Dde)-Pro-Gly-Lys(Aloc)-Ala-OH (1.11 g, 0.60mmol) was dissolved in DMF (600mL) and the pH adjusted to 8-9 by addition of DIPEA. HATU (0.26g, 1.1 equiv) was added and the soln was stirred at rt for 3 h. The solvent was removed under high vacuum and the residue was dissolved in TFA/CH2C12 (1 1,70mL) and allowed to stand at rt for 45 min. The soln was concentrated under reduced pressure and the residue triturated with Et20. Filtration afforded crude product yield 0.94 g purity >90%. The crude product (780 mg, -75%) was dissolved in MeCN/H20 (1 1) and the pH raised to 7-8 by addition of collidine (180 pL). Solid-phase extraction (Sep-Pak Vac cartridge, C18,15 mL) and lyophilization afforded the collidine salt of the title compound (750 mg) and was directly used for the immobilization reaction. 

The diamine 2 was added to an etherial solution of an acyl chloride 1 in a Teflon-capped vial. Salt precipitaion was instant. The solvent was removed by filtration, where the Teflon cap served as the filter. Lawesson s reagent (1.0-1.5 equiv.) was added to the salt 3 and the resulting mixture of solids was mixed thoroughly and thereafter irradiated for 8 min in a domestic microwave oven (900 W, Whirlpool M401). Solid-phase extraction afforded the thioamides 4 in adequate purities and yields. 

S. Lacorte, J. J. Vreuls, J. S. Salau, F. Ventura and D. Barcelo, Monitoring of pesticides in river water using fully automated on-line solid-phase extraction and liquid chromatography with diode array detection with a novel filtration device , J. Chromatogr. 795 71-82(1998). 

SFE—Separation and filtration cartridge column. Also referred to as a SPE (solid phase extraction column). (See windowing in Chapter 12.)... 

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