Sample preparation solvent

Freshly distilled diethylmalonate (DEM) was used as a solvent. SAMPLE PREPARATION... 

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). 

Recently, SPE cartridges and disks have been widely and successfully used in preconcentration processes [1-3]. They reduce solvent usage, disposal costs, and extraction time for sample preparation and obtain large enrichment factors. 

Results found by the NIR method compared well with those obtained by the reference chromatographic procedures. The developed PLS/NIR method does not consume any solvent as no sample preparation is necessary, improving the laboratory efficiency without sacrifice the accuracy. 

Theoretical and applied aspects of microwave heating, as well as the advantages of its application are discussed for the individual analytical processes and also for the sample preparation procedures. Special attention is paid to the various preconcentration techniques, in part, sorption and extraction. Improvement of microwave-assisted solution preconcentration is shown on the example of separation of noble metals from matrix components by complexing sorbents. Advantages of microwave-assisted extraction and principles of choice of appropriate solvent are considered for the extraction of organic contaminants from solutions and solid samples by alcohols and room-temperature ionic liquids (RTILs). 

Elimination of sample preparation and handling of toxic solvents such as carbon disulphide Absence of solvent simplifies chromatograph Increased sensitivity Sample tubes can be reused ... 

Large quantities of solvents are employed for sample preparation, in particular, and these are then concentrated down to a few milliliters. So particularly high quality materials that are as free as possible from residual water and especially free from nonvolatile or not readily volatile impurities ought to be employed here such impurities are enriched on concentration and can lead to gross contamination. The same considerations also apply to preparative chromatography. Special solvents of particular purity are now available. 

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.). 

Although SFE and SFC share several common features, including the use of a superaitical fluid as the solvent and similar instrumentation, their goals are quite distinct. While SFE is used mainly for the sample preparation step (extraction), SFC is employed to isolate (chr-omatography) individual compounds present in complex samples (11 -15). Both techniques can be used in two different approaches off-line, in which the analytes and the solvent are either vented after analysis (SFC) or collected (SFE), or on-line coupled with a second technique, thus providing a multidimensional approach. Off-line methods are slow and susceptible to solute losses and contamination the on-line coupled system makes possible a deaease in the detection limits, with an improvement in quantification, while the use of valves for automation results in faster and more reproducible analyses (16). The off-line... 

In Figure 8-1 we show the chemical structure of m-LPPP. The increase in conjugation and the reduction of geometrical defects was the main motivation to incorporate a poly(/ -phenylene)(PPP) backbone into a ladder polymer structure [21]. Due to the side groups attached to the PPP main chain excellent solubility in nonpolar solvents is achieved. This is the prerequisite for producing polymer films of high optical quality. A detailed presentation of the synthesis, sample preparation,... 

Margarine is an example of a solid sample where the materials of interest are soluble in one solvent (in this case methanol) whereas the matrix materials, largely triglycerides, are not. As a consequence, the sample preparation procedure is relatively simple. The chromatographic separation is achieved by using the dispersive interactions between the hydrocarbon chains of the fatty acids and the hydrocarbon chains of a reversed phase. 

This sample preparation required both extraction and concentration and this was carried out in the traditional manner with the use of an appropriate solvent. The separation was again achieved exploiting the dispersive interactions between the components of the mixture and the strongly dispersive hydrocarbon chains on the reversed phase. 

The sample preparation was very simple the sample was centrifuged to remove plant cell residues and 10 pi of the clear juice was placed on the column. This type of separation is common with fruits, vegetables and juices and samples can be obtained by preliminary homogenizing the total tissues and then centrifuging. If it is suspected that the residue still contains significant quantities of the substances of interest, then it can be washed with water or if necessary with solvents and the washings combined with the separated supernatant liquor. The results obtained are shown in figure 15. 

The use of other important phase systems such as exclusion media, ion exchange media and polar stationary phases such as silica gel have not been discussed as this chapter is primarily concerned with sample preparation. The last chapter will give examples of the use of these other phase systems and explain the separations obtained on a basis of molecular interactions and, at that time, the subject of solvent choice will again be discussed. 

The primary method for detecting methyl parathion and metabolites in biological tissues is gas chromatography (GC) coupled with electron capture (BCD), flame photometric (FPD), or flame ionization detection (FID). Sample preparation for methyl parathion analysis routinely involves extraction with an organic solvent (e g., acetone or benzene), centrifugation, concentration, and re suspension in a suitable solvent prior to GC analysis. For low concentrations of methyl parathion, further cleanup procedures, such as column chromatography on silica gel or Florisil are required. 

Richter, B.E. et al.. Accelerated solvent extraction a technique for sample preparation. Anal. Chem., 68, 1033, 1996. 

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