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Capping artifact

FIGURE 16.8 These three artifacts represent the progress that has been made in the extraction of d-metals. (a) An ancient bronze chariot axle cap from China made from an alloy of metals that are easy to extract, (b) An early iron steam engine made from a metal that was moderately easy to extract once high temperatures could be achieved, (c) A twentieth-century airplane engine with titanium components that had to await high temperatures and advanced technology before the element became widely available. [Pg.900]

Note 2 A vial with a plastic cap other than one made of Teflon should not be used This is of primary importance in obtaining a clean gas chromatogram, 1 e, a gas chromatogram free of GC peaks for artifacts Otherwise, plasticizers such as bis(2-ethylhexyl)phthalate in the plastic cap will dissolve in the sample solution The presence of such artifacts in the sample solution also affects the resolution of GC peaks in the gas chromatograms and the mass spectra obtained from GC-MS analysis as well... [Pg.309]

Note 2. The glacial acetic acid used was reagent grade and methanol and water were HPLC grade. The use of well-cleaned glassware with inert caps and seals is necessary to eliminate artifacts. [Pg.396]

The combined 0.1 N HCl fractions are adjusted to pH 9 with 1 N aqueous ammonia followed by reextraction of the alkaloids three times into chloroform, each time with one-half volume of chloroform. The combined chloroform layers are dried over Na2S04 and then evaporated to dryness at 30°C in vacuo with a water aspirator. Many of the dendrobatid alkaloids have appreciable volatility, and evaporation in vacuo must be done carefully. The resulting alkaloid residue is dissolved in methanol so that 100 (A corresponds to 100 mg of original wet weight of skin, then stored at -20°C in glass vials with Teflon-lined caps. This alkaloid fraction contains mainly alkaloids, but traces of fatty acid methyl esters, steroids, and environmental artifacts, such as phthalates and phenolic antioxidants, often are present as minor contaminants. [Pg.281]

Formyl derivatives are also popular in situations where several groups have to be blocked, as in steroid analysis, because the formyl group adds little to the molecular weight. To prevent the formation of artifacts, the strength of the formic acid should be kept at 95% and reaction allowed to take place for 30 min at 40°C. Alternatively, sodium formate can be used, an example of which is in the preparation of the enol rert-butyldi-methylsilyl derivatives of steroids and bile acids. Sodium formate solution (1 mg in 100 p,l) is dried under a stream of nitrogen in a 1 ml reaction tube fitted with a Teflon-lined screw cap. The tube is then heated to 270°C for 30 min, cooled, and 10 p,g of the steroid in 100 p,l of methanol added. The solvent is evaporated under a stream... [Pg.2250]


See other pages where Capping artifact is mentioned: [Pg.39]    [Pg.39]    [Pg.101]    [Pg.77]    [Pg.306]    [Pg.244]    [Pg.68]    [Pg.296]    [Pg.138]    [Pg.38]    [Pg.233]    [Pg.189]    [Pg.292]    [Pg.62]    [Pg.798]    [Pg.357]    [Pg.363]    [Pg.231]    [Pg.1730]    [Pg.909]    [Pg.910]    [Pg.41]    [Pg.220]    [Pg.75]    [Pg.511]    [Pg.38]    [Pg.226]    [Pg.330]   
See also in sourсe #XX -- [ Pg.39 ]




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