Sample preparation evaporation

Sample preparation Evaporate solution (eluate from preparative HPLC) to dryness under a stream of nitrogen, reconstitute with 10 pL 2 pg/mL 9-anthroylnitrile (Wako) in MeCN and 10 pL triethylamine MeCN 30 70 under nitrogen, let stand at room temperature for 20 min, add 5 pL water, after 6 min add 50 pL 600 mM acetic acid in MeCN, evaporate to dryness under a stream of nitrogen at 37°, reconstitute with 90 pL MeOH ... 

Sample preparation Evaporate to dryness imder reduced pressure, reconstitute, inject an aliquot. 

Sample preparation Evaporate 100 [xL 1 p,g/mL IS in MeOH in the bottom of a tube using a stream of nitrogen, add 1 mL whole blood, add 1 mL buffer, vortex for 1 min, add 5 mL dichloromethane hexane ethyl acetate 50 40 10, shake horizontally at 200 cycles/min for 30 min, centrifuge at 2000 rpm for 30 min. Evaporate the organic layer to dryness under a stream of nitrogen, reconstitute the residue with 100 xL initial mobile phase, inject an aliquot. (Prepare the buffer by adjusting the pH of 1 L saturated ammonium chloride solution to 9.5 with 25% ammonium hydroxide.)... 

Most fiindamental surface science investigations employ single-crystal samples cut along a low-index plane. The single-crystal surface is prepared to be nearly atomically flat. The surface may also be modified in vacuum. For example, it may be exposed to a gas that adsorbs (sticks) to the surface, or a film can be grown onto a sample by evaporation of material. In addition to single-crystal surfaces, many researchers have investigated vicinal, i.e. stepped, surfaces as well as the surfaces of polycrystalline and disordered materials. 

The polyethylene crystals shown in Fig. 4.11 exist as hollow pyramids made up of planar sections. Since the solvent must be evaporated away prior to electron microscopic observation, the pyramids become buckled, torn, and/ or pleated during the course of sample preparation. While the pyramidal morphology is clearly evident in Fig. 4.1 la, there is also evidence of collapse and pleating. Likewise, the ridges on the apparently planar crystals in Fig. 4.1 lb are pleats of excess material that bunches up when the pyramids collapse. 

Preparation of soil—sediment of water samples for herbicide analysis generally has consisted of solvent extraction of the sample, followed by cleanup of the extract through Uquid—Uquid or column chromatography, and finally, concentration through evaporation (285). This complex but necessary series of procedures is time-consuming and is responsible for the high cost of herbicide analyses. The advent of soUd-phase extraction techniques in which the sample is simultaneously cleaned up and concentrated has condensed these steps and thus gready simplified sample preparation (286). 

Extended x-ray absorption fine stmcture measurements (EXAFS) have been performed to iavestigate the short-range stmcture of TbFe films (46). It is observed that there is an excess number of Fe—Fe and Tb—Tb pairs ia the plane of the amorphous film and an excess number of Tb—Fe pairs perpendicular to film. The iacrease of K with the substrate temperature for samples prepared by evaporation is explained by a rearrangement of local absorbed atom configurations duting the growth of the film (surface-iaduced textuting) (47). 

Reduction of 17a-EthynyI to 17a-Ethyl °° A solution of 5 g of 17a-ethynyl-androst-5-ene-3j9,17j5-diol in 170 ml of absolute alcohol is hydrogenated at atmospheric pressure and room temperature using 0.5 g of 5 % palladium-on-charcoal catalyst. Hydrogen absorption is complete in about 8 min with the absorption of 2 moles. After removal of the catalyst by filtration, the solvent is evaporated under reduced pressure and the residue is crystallized from ethyl acetate. Three crops of 17a-ethylandrost-5-ene-3) ,17j9-diol are obtained 3.05 g, mp 197-200° 1.59 g, mp 198.6-200.6° and 0.34 g, mp 196-199° (total yield 5.02 g, 90%). A sample prepared for analysis by recrystallization from ethyl acetate melts at 200.6-202.4° [aj, —70° (diox.). 

The mycelium (56 g dry weight) was filtered off and the steroidal material was extracted with methylene chloride, the methylene extracts evaporated to dryness, and the resulting residue chromatographed over a Florisil column. The column was packed with 200 g of Florisil and was developed with five 400-ml fractions each of methylene chloride, Skelly-solve 8-acetone mixtures of 9 1, 8 2, 7 3, 1 1, and methanol. The fraction eluted with Skellysolve 8-acetone (7 3) weighed 1.545 g and on recrystallization from acetone gave, in three crops, 928 mg of product of MP 210° to 235°C. The sample prepared for analysis melted at 245° to 247°C. 

Sample preparation Dried greater celandine was pulverized and briefly boiled in 0.05 mol sulfuric acid. After cooling to room temperature the mixture was placed in a separating funnel and adjusted to pH 10 with ammonia solution and extracted once with chloroform. The organic phase was dried with sodium sulfate and evaporated to dryness under reduced pressure. The residue was taken up in methanol and used as the sample solution for TLC. 

Kennedy et al. developed a lasalocid immunoassay for application to residues in chicken meat and liver samples. The antibody was specific and did not cross-react with salinomycin, maduramicin, or monensin. Sample preparation consisted of homogenization in aqueous acetonitrile, removal of fat from an aliquot of the aqueous acetonitrile by hexane extraction, and evaporation of acetonitrile. The sample was then reconstituted with assay buffer. Liver required an additional solid phase extraction step. The LOQ was 0.02 xgkg for muscle and 0.15 agkg for liver. These workers were able to use the system to determine the half-life of lasalocid in the tissues. 

Ivermectin, a macrocyclic lactone, is also utilized to control parasites. An immunoassay was developed to determine ivermectin residues in bovine liver by Crooks etal. The sample preparation procedure was complex, involving tissue homogenization in acetonitrile, centrifugation, extraction with hexane (to remove lipids), evaporation and reconstitution in ethyl acetate, and passage through an SPE column followed... 

SFE of fruits and vegetables and meat products has been reported, but the sample preparation techniques necessary to obtain reproducible results are extremely time consuming. Solid absorbents such as Hydromatrix, Extrelut " anhydrous magnesium sulfate or absorbent polymers are required to control the level of water in the sample for the extraction of the nonpolar pesticides. Without the addition of Hydromatrix, nonpolar pesticides cannot penetrate the water barrier between the sample particles and the supercritical CO2. The sample is normally frozen and the addition of dry-ice may be required to reduce losses due to degradation and/or evaporation. Thorough reviews of the advantages and limitations of SFE in pesticide residues... 

Solubilizing all or part of a sample matrix by contacting with liquids is one of the most widely used sample preparation techniques for gases, vapors, liquids or solids. Additional selectivity is possible by distributing the sample between pairs of immiscible liquids in which the analyte and its matrix have different solubilities. Equipment requirements are generally very simple for solvent extraction techniques. Table 8.2 [4,10], and solutions are easy to manipulate, convenient to inject into chromatographic instruments, and even small volumes of liquids can be measured accurately. Solids can be recovered from volatile solvents by evaporation. Since relatively large solvent volumes are used in most extraction procedures, solvent impurities, contaminants, etc., are always a common cause for concern [65,66]. 

Industrial analytical laboratories search for methodologies that allow high quality analysis with enhanced sensitivity, short overall analysis times through significant reductions in sample preparation, reduced cost per analysis through fewer man-hours per sample, reduced solvent usage and disposal costs, and minimisation of errors due to analyte loss and contamination during evaporation. The experience and criticism of analysts influence the economical aspects of analysis methods very substantially. 

On-line coupled sample preparation/separation/iden-tification systems (e.g. SFE-GC, PFE/automated evaporation/HPLC). 

Gas chromatographic analysis starts with introduction of the sample on the column, with or without sample preparation steps. The choice of inlet system will be dictated primarily by the characteristics of the sample after any preparation steps outside the inlet. Clearly, sample preparation has a profound influence on the choice of injection technique. For example, analysts may skip the solvent evaporation step after extraction by eliminating solvent in the inlet with splitless transfer into the column. Sample introduction techniques are essentially of two types conventional and programmed temperature sample introduction. Vogt et al. [89] first described the latter in 1979. Injection of samples, which... 

Major advantages of LVI methods are higher sensitivity (compare the 100-1000 iL volume in LVI to the maximum injection volume of about 1 iL in conventional splitless or on-column injection), elimination of sample preparation steps (such as solvent evaporation) and use in hyphenated techniques (e.g. SPE-GC, LC-GC, GC-MS), which gives opportunities for greater automation, faster sample throughput, better data quality, improved quantitation, lower cost per analysis and fewer samples re-analysed. At-column is a very good reference technique for rapid LVI. Characteristics of LVI methods are summarised in Tables 4.19 and 4.20. Han-kemeier [100] has discussed automated sample preparation and LVI for GC with spectrometric detection. 

SFE-GC-MS is particularly useful for (semi)volatile analysis of thermo-labile compounds, which degrade at the higher temperatures used for HS-GC-MS. Vreuls et al. [303] have reported in-vial liquid-liquid extraction with subsequent large-volume on-column injection into GC-MS for the determination of organics in water samples. Automated in-vial LLE-GC-MS requires no sample preparation steps such as filtration or solvent evaporation. On-line SPE-GC-MS has been reported [304], Smart et al. [305] used thermal extraction-gas chromatography-ion trap mass spectrometry (TE-GC-MS) for direct analysis of TLC spots. Scraped-off material was gradually heated, and the analytes were thermally extracted. This thermal desorption method is milder than laser desorption, and allows analysis without extensive decomposition. 

SEC in combination with multidimensional liquid chromatography (LC-LC) may be used to carry out polymer/additive analysis. In this approach, the sample is dissolved before injection into the SEC system for prefractionation of the polymer fractions. High-MW components are separated from the additives. The additive fraction is collected, concentrated by evaporation, and injected to a multidimensional RPLC system consisting of two columns of different selectivity. The first column is used for sample prefractionation and cleanup, after which the additive fraction is transferred to the analytical column for the final separation. The total method (SEC, LC-LC) has been used for the analysis of the main phenolic compounds in complex pyrolysis oils with minimal sample preparation [974]. The identification is reliable because three analytical steps (SEC, RPLC and RPLC) with different selectivities are employed. The complexity of pyrolysis oils makes their analysis a demanding task, and careful sample preparation is typically required. 

Figure 6. Plan of the target preparation facilities consisting of UHV preparation chamber (a), (reactive) ion etching chamber (b), ion etching gun (c), laser (d), photon detector (e), transfer arms (f), Auger system for surface analysis (g), sample manipulator and annealing facility (h), load lock and optical microscope for viewing sample (i), evaporator (j), transmission diffractometer (k), and vacuum tank for main spectrometer (1).

Because plasma and urine are both aqueous matrixes, reverse-phase or polar organic mode enantiomeric separations are usually preferred as these approaches usually requires less elaborate sample preparation. Protein-, cyclodextrin-, and macrocyclic glycopeptide-based chiral stationary phases are the most commonly employed CSPs in the reverse phase mode. Also reverse phase and polar organic mode are more compatible mobile phases for mass spectrometers using electrospray ionization. Normal phase enantiomeric separations require more sample preparation (usually with at least one evaporation-to-dryness step). Therefore, normal phase CSPs are only used when a satisfactory enantiomeric separation cannot be obtained in reverse phase or polar organic mode. 

Prange et al. [809,810] carried out multielement determinations of the stated dissolved heavy metals in Baltic seawater by total reflection X-ray fluorescence (TXRF) spectrometry. The metals were separated by chelation adsorption of the metal complexes on lipophilised silica-gel carrier and subsequent elution of the chelates by a chloroform/methanol mixture. Trace element loss or contamination could be controlled because of the relatively simple sample preparation. Aliquots of the eluate were then dispersed in highly polished quartz sample carriers and evaporated to thin films for spectrometric measurements. Recoveries (see Table 5.10), detection limits, and reproducibilities of the method for several metals were satisfactory. 

All of the samples analyzed were standard one-inch diameter polished thin sections. Whenever feasible the samples received a final, cleansing polish with 1 pm diamond compound made from commercial graded diamonds embedded in "vaseline". Commercial diamond paste has proved unsatisfactory due to high levels of K, Na, Cl, Si, F, and Ca. Samples are then cleaned with carbon tetrachloride, rinsed in ethanol, and coated with vacuum evaporator. This sample preparation technique was developed during our studies of minor elements [16,17] and has proved to produce consistently contamination-free samples. 

The study concluded that Once wash steps are optimized, samples prepared by solid phase extraction are cleaner than those prepared by protein precipitation. Samples prepared by extraction with a Multi-SPE plate resulted in lower LOQs than samples prepared by solvent precipitation. Drug recoveries were acceptable (>80%) for both the SPE and the solvent precipitation methods. Well-to-well reproducibility of samples was slightly better with extraction with a Multi-SPE plate. Evaporation and reconstitution, while more time-consuming, yield better chromatographic performance, allow analysis of lower concentration samples, and require optimization for good analyte recovery. 

Recovery — Overall procedural recovery was evaluated. The results from spiked plasma QC (evaluation) samples that went through the analytical procedure were compared to the results from neat spiking (control) solution samples. The neat spiking solutions used to prepare the plasma evaluation samples were evaporated and reconstituted at the same volumes as the extracted samples. The analyte was tested at three concentration levels and the internal standard was tested at one. Mean recovery for the analyte was approximately 122.9% the level was 55.2% for the internal standard. 

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