Conventional preparation method, rapid

Two serious drawbacks of this method are the extensive deuterium scrambling around the reaction site and the occasional formation of olefinic side products, which are hard to separate by conventional means. The extent of olefin formation may depend on the nature of the Raney nickel since it is known that desulfurization with deactivated Raney nickel can yield olefins. Best results are obtained when the deuterated Raney nickel is prepared very rapidly and used immediately after preparation. 

Polymer modification is of particular interest when the desired polymer is not readily available from its corresponding monomer by conventional polymerization methods. The primary challenge of polymer modification is to achieve a high conversion and selective modification of the appropriate functional group. In this paper, we describe a new convenient polymer modification to prepare novel silanol polymers by a rapid and selective oxidation of the Si—H bond with a dimethyldioxirane solution in acetone from their corresponding precursor polymers. 

Another example in the literature on the preparation of pure polymorphic forms of drug compounds by SCF processing is that of fluticasone propionate, which is also a drug delivered by the respiratory route (27). As the compound decomposes before melting, DSC traces do not give definitive temperature profiles for the transformation between polymorphs I and II. X-ray diffraction patterns, however, have been used to confirm the presence of different polymorphic forms. The drug recrystallizes as form II from solution by the SEDS process in the presence of supercritical carbon dioxide at all temperatures, while form I is obtained by conventional crystallization methods. The rapid nucleation by SCF antisolvent aids in the formation of the metastable form II. A further advantage of SCF... 

The SHS method is expected to be developed as a process for producing new materials from composite powders and solid solutions that are difficult to prepare by conventional synthesis methods. By varying the combustion synthesis parameters, the properties of the product can be tailored to meet specific application needs. The combustion-consolidation method makes it possible to change the metal composition in the ceramic matrix because the initial arrangement of compositional constituents of the green body remains in the product due to the rapid wave propagation of the combustion reaction. 

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. 

The results for bacterial whole-cell analysis described here establish the utility of MALDI-FTMS for mass spectral analysis of whole-cell bacteria and (potentially) more complex single-celled organisms. The use of MALDI-measured accurate mass values combined with mass defect plots is rapid, accurate, and simpler in sample preparation then conventional liquid chromatographic methods for bacterial lipid analysis. Intact cell MALDI-FTMS bacterial lipid characterization complements the use of proteomics profiling by mass spectrometry because it relies on accurate mass measurements of chemical species that are not subject to posttranslational modification or proteolytic degradation. 

Recently, comparatively inexpensive, very reliable, and stable single quadrupole mass spectrometers have entered the market. These spectrometers can be coupled to GC, LC, and CE separation methods simply by modifying the sampling interfaces. Although these detectors are more expensive than most conventional detectors including the versatile electron capture and diode array absorbance detectors used for GC and LG respectively, the reduction in sample preparation effort and their increased specificity can often rapidly... 

Fig. 3 TEM micrographs of Mg/Al - CO3 LDHs with different Mg /Al ratios prepared using the new method using rapid mixing and nucleation in a colloid mill followed by a separate aging step (a-c) and conventional coprecipitation at constant pH (d-f). The new method affords smaller crystallites with a much narrower range of length. Reprinted with permission from [20]. Copyright ACS Journal Archives...

Colloidal potassium has recently been proved as a more active reducer than the metal that has been conventionally powdered by shaking it in hot octane (Luche et al. 1984, Chou and You 1987, Wang et al. 1994). To prepare colloidal potassium, a piece of this metal in dry toluene or xylene under an argon atmosphere is submitted to ultrasonic irradiation at ca. 10°C. A silvery blue color rapidly develops, and in a few minutes the metal disappears. A common cleaning bath (e.g., Sono-clean, 35 kHz) filled with water and crushed ice can be used. A very fine suspension of potassium is thus obtained, which settles very slowly on standing. The same method did not work in THF (Luche et al. 1984). Ultrasonic waves interact with the metal by their cavitational effects. These effects are closely related to the physical constants of the medium, such as vapor pressure, viscosity, and surface tension (Sehgal et al. 1982). All of these factors have to be taken into account when one chooses a metal to be ultrasonically dispersed in a given solvent. 

---