Sample preparation mixed solvents

Sample preparation Mix 500 jiL plasma with 50 iL 1 M KOH, add 25 JiL 20 jig/mL IS in MeCN, add 3 mL extraction solvent, vortex for 1 min, centrifuge at 1000 g for 10 min, fi-eeze the aqueous layer, remove the organic layer, repeat the extraction. Evaporate the combined organic layers to dryness under reduced pressure, reconstitute the residue with 200 (jiL MeCN 50 mM pH 7.0 ammonium acetate buffer 50 50, centrifuge, inject an aliquot of the supernatant. (Extraction solvent was n-hcxanc isopropanol dimcthyloctylamine 98 2 0.1.)... 

Samples for studies of CDx effects on fluorescence enhancement in organic solution were prepared using pyrene, because pyrene possesses a long lifetime and is very susceptible to quenching and enhancement in solution (23). An aliquot of pyrene stock solution in cyclohexane was placed under a nitrogen purge to evaporate the cyclohexane. Samples were redissolved in a 1 A mixture of Isopropyl ether and 1-butanol, which was saturated with aqueous CDx solution. Pyrene samples were also prepared in which the organic solvent was not saturated with CDx solution. The mixed solvent was used in order to minimize the effects of ether evaporation and thus allow more accurate quantitation. Fluorescence measurements were made on diluted samples of these solutions. The solvent used to make up the... 

Transfer the residue with 1 g of Florisil PR on to the top of the column packed with 9 g of Florisil PR with the aid of hexane. Rinse the column with 150 mL of hexane-acetone (4 1, v/v). Elute acetamiprid with 120 mL of a mixed solvent of acetone-hexane (1 1, v/v) and concentrate the eluate to near dryness by rotary evaporation at 40 °C. Dissolve the residue with 5 mL of distilled water and apply the solution to the top of the packed Sep-Pak Ci8 column pretreated with 20 mL each of methanol and distilled water. Elute acetamiprid with 30 mL of a mixed solution of water-acetonitrile (17 3, v/v). Concentrate to dryness on a water-bath at ca 40 °C by rotary evaporation. Prepare the GC-ready sample by dissolving the residue in acetone. 

An alternative system proved to be both simpler and more user friendly (Unger et al., 2004 Machtejevas et al., 2006). Thus far we have used this configuration to analyze human plasma, sputum, urine, cerebrospinal fluid, and rat plasma. For each particular analysis we set up an analytical system based on a simple but specific strategy (Figure 9.5). The analysis concept is based on an online sample preparation and a two-dimensional LC system preseparating the majority of the matrix components from the analytes that are retained on a RAM-SCX column followed by a solvent switch and transfer of the trapped peptides. The SCX elution used five salt steps created by mixing 20 mM phosphate buffer (pH 2.5) (eluent Al) and 20 mM phosphate buffer with 1.5 M sodium chloride (eluent Bl) in the following proportions 85/15 70/30 65/45 45/55 0/100 with at the constant 0.1 mL/min flow rate. Desorption of the... 

This microparallel analysis provides the ability to analyze a large number of compounds, increase the number of replicates or conditions used in a study, and reduce solvent consumption and mixed waste generation. Nanostream, Inc. has developed instrumentation for pPl.C with different capabilities suited for diverse applications (e.g., the Nanostream CL system for high-throughput LC, the Nanostream LD for assay detection, and the Nanostream CX for sample preparation). 

All reagents and solvents were used as received (Sigma-Aldrich) if not stated otherwise. NOL-130 stab initiation mix and preformed, 19 mg graphite-blended l,3,5-trinitro-l,3,5-triazacyclohexane (RDX) pellets were purchased from Day Zimmerman (DZI). Samples prepared for LC-MS analysis were dissolved in ammonium hydroxide and run utilizing a Phenomenex Gemini C6-Phenyl column (4.6 mm X 150 mm) and a mobile phase of 20 mM ammonium acetate in water pH 7.02 at 0.75 ml,-min The HPLC analysis is done using... 

A pivotal step in the analytical process is sample preparation. Frequently liquid-liquid extractions (LLEs) are used. Solvents, pH, and multiple back extractions are all manipulated to increase selectivity and decrease unwanted contaminants before injection on the GC system. Solid phase extraction (SPE) is more convenient than it used to be because of an increase in commercially available SPE columns. SPE columns are packed with an inert material that binds the drug of interest, allowing impurities to pass through. As with LEE, solvent choices and pH affect retention and recovery. There are three commercially available types of SPE columns, diatomaceous earth (which uses the same principles as LLE), polystyrene-divinylbenzene copolymer, and mixed mode bonded silica (Franke and de Zeeuw, 1998). 

Experimentally a cyanate ester precursor mixture consisting of BPEC, 1 wt % BPE, and 100 ppm cobaltacetylacetonate was prepared and subsequently mixed with the cyclohexane phase separating solvent [86]. Essentially the same procedure as for the epoxy is used for sample preparation with the difference that the curing was done at 80 °C and post drying at 240 °C. 

In a 50-ml centrifuge tube with cap, carefully measure the prepared food sample and mix it with solvent (i.e., acetonitrile, HC1, and water) as detailed in Table 11.6.2. Break up cellular material using an ultrasonic bath for 10 min. 

Moret et al. (67,68) studied all the parameters that influence amine recovery under conditions where a liquid-liquid purification step with an organic solvent follows the acid extraction, prior to derivatization with DBS and RP-HPLC analysis. The optimized methods of sample preparation for different foods, including cheese, meat, and fish, are given. The same research group (69) optimized the extraction conditions for Phe, Put, Cad, His, Tyr, Spe, and Spd. Food samples were first mixed with TCA and centrifuged and then basified and extracted with BuOH/CHCl3 (1 1). The BAs were then derivatized with DNS and separated on a Spherisorb 3S TG column with an ACN-H20 gradient. The method was applied to samples of tuna, salmon, and salami. 

A major problem in liquid-liquid extraction for sample preparation is emulsion formation which leads to lower recoveries. Emulsions occur readily when solvents of similiar densities are mixed and when extraction solutions are highly basic. 

Different reversed phase [195,239,240], mixed mode (ion exchange and reversed phase) SPE cartridges [173,218] and online SPE column [193, 238] have been also reported for samples preparation and extraction. Some of these assays combined both PP and SPE in order to achieve an extensive sample cleanup [193, 195, 238-240], Likewise SPE, LLE provides cleaner plasma extracts than PP. Nevertheless, LLE procedure does not always provide satisfactory results with regard to extraction recovery and selectivity, especially with polar analytes and particularly in the case of multicomponent analysis such as in drug-metabolism studies, where analytes polarity varies widely. This issue was addressed by Zweigenbaum J and Henion J [235] and extraction solvent optimization, using isoamyl alcohol, to achieve acceptable extraction selectivity and recovery for polar analytes has been discussed. 

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