Purification methods solid-phase extraction

In order to study simultaneously the behaviour of parent priority surfactants and their degradation products, it is essential to have accurate and sensitive analytical methods that enable the determination of the low concentrations generally occurring in the aquatic environment. As a result of an exhaustive review of the analytical methods used for the quantification within the framework of the three-year research project Priority surfactants and their toxic metabolites in wastewater effluents An integrated study (PRISTINE), it is concluded that the most appropriate procedure for this purpose is high-performance (HP) LC in reversed phase (RP), associated with preliminary techniques of concentration and purification by solid phase extraction (SPE). However, the complex mixtures of metabolites and a lack of reference standards currently limit the applicability of HPLC with UV- or fluorescence (FL-) detection methods. 

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 contrast to liquid-liquid partitioning cleanup, which is particularly suitable for individual drugs or groups of drugs with similar chemical properties, solid-phase extraction is more appropriate for multiresidue analysis. On that account, solid-phase extraction in combination with liquid-liquid partitioning has become the method of choice in many laboratories for the purification of residues of sedatives and -blockers that may occur in biological matrices. Purification is usually accomplished on reversed-phase solid-phase extraction columns. Optimum retention of seven sedatives and carazolol on a reversed-phase solid-phase extraction column was reported when 10% sodium chloride solution was added to the acetonitrile hssue extract prior to its solid-phase extrachon cleanup (523, 524). A silica-based diol solid-phase extraction column was further suggested for efficient isolation of sedative and -blocker residues from food extracts (526). 

In a method proposed by Booth et al. (141) for the determination of phylloquinone in various food types, extracted samples are subjected to silica solid-phase extraction followed, in the case of meat or milk samples, by further purification using reversed-phase solid-phase extraction or liquid-phase reduction extraction, respectively. The final test solution is analyzed by NARP-HPLC, and the fluorescent hydroquinone reduction products of phylloquinone and the internal standard are produced online using a postcolumn chemical reactor packed with zinc metal. 2, 3 -Dihydrophylloquinone, a synthetic analog of phylloquinone, is a suitable internal standard for the analysis of vegetable juice, whole milk, and spinach. Another synthetic analog, Ku23), is used for the analysis of bread and beef, because a contaminant in the test solution coelutes with dihydro-phylloquinone. 

Seeberger and coworkers prepared synthetically useful amounts of P-peptides (0.2-0.6mmol) by using a microreactor (reactor volume = 78.3 pi). The reaction of add fluoride and the TFA salt of amino acid benzyl ester in the presence of N-methylmorpholine (NMM) at 90 °C (3 min residence time) gave the dipeptide in 92% yield (Scheme 4.19). A fluorous tag method was used for an effident synthesis of tetrapeptides. Amino acid esters having fluorous tags were used to facilitate purification by fluorous solid-phase extraction (FSPE) (Scheme 4.20). 

DNA extraction and purification were traditionally accomplished using organic extraction and ultracentrifugation-based procedures, which are both time-consuming and not easily transferable to the microscale. Newer methods employ solid-phase extraction (SPE) on silica surfaces, glass fibers, modified magnetic beads, and ion-exchange resins—techniques that save time and are also more amenable to chip applications. 

Determination of free 4-hydroxy-2,3-trans-alkenals by HPLC Esterbauer (1982) has developed a procedure for the qualitative detection and quantitative measurement of steady-state concentrations of free hydroxyalkenals (specifically HNE) in tissues, tissue extracts and lipid containing foodstuffs. Their method utilizes UV-detection of the free aldehyde at its 220 nm UV-absorption maximum and peak identification was confirmed by mass spectrometry. An effective purification and concentration step is employed using dichloromethane to extract hydroxyalkenals from samples trapped on Extrelut columns. The samples are subsequently purified by solid-phase extraction on octadecyl-bonded silica (ODS) disposable cartridges and then analysed by HPLC. 

Within the pharmaceutical industry there has always been a need for sample purity. Any compound that is a potential drug candidate can only be fully characterised and tested once it is available in a pure form. There are many purification tools available for sample clean-up, e.g. flash chromatography, solid phase extraction, etc. 1-31. However, for the more complex purification problems where the desired compound and its associated contaminants have very similar polarities, structures, etc., preparative chromatography is the method of choice due to its superior separative capabilities. Preparative chromatography can also be scaled up from lens of milligrams to tens or even hundreds of grams of compound. The other main factor in favour of this technique is its ability to be tailored for most classes of compound. 

A purification method for microcystins in lake water consists of solid-phase extraction on a Sep-Pak PS2 ... 

Methods of analysis by direct injection in the column of sample were proposed (Lea et al., 1979 Nagel et al., 1979 Ong and Nagel, 1978 Wulf and Nagel, 1976 Roggero et al., 1989 Lamuela-Raventos and Waterhouse, 1994), but usually, prior to analysis, the different classes of compounds are fractionated on absorbent polymers such as polyamide, Sephadex LH20 or C18. The stationary phase C18 is also used for concentration and purification of the sample by solid phase extraction (SPE) prior to analysis. 

Preliminary extraction of 5-HIAA may be used as an initial purification step before HPLC analysis. Organic solvents, anion-exchange resins, and other solid phase extraction procedures have aU been used. For many systems, direct injection of urine onto the analytical column is a common practice,and samples are often merely diluted with a buffer to protect the HPLC system from contamination. Methods that analyze 5-HIAA without prior sample cleanup rely on the selectivity of the HPLC separation combined with fluorescence or electrochemical detection to provide the requisite specificity. 

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