Directly Transferring Nitrogen

Cryoelectron microscopy makes it possible to have a direct view into the frozen sample without additional preparation [100]. With the aid of a cryogen (e.g., liquid nitrogen-cooled liquid ethane), the sample is plunge frozen as a very thin aqueous film prepared on a microscopic grid. Subsequently, the vitrified specimen is directly transferred into a precooled electron microscope. Because the specimens are usually ) 2005 by CRC Press LLC... 

Protein Determine as directed under Nitrogen Determination, Appendix EIC, transferring about 3.5 g of sample, accurately weighed, into a 500-mL Kjeldahl flask. The percent of protein equals the percent of N x 6.25. 

Due to their highly polar nature, barbiturates require derivatization prior to analysis by GC-MS. In such cases, the sample is dissolved in methanol, centrifnged, the supernatant recovered and placed in a derivatizing vial and is then blown down under nitrogen. The derivatization procednre, using 0.2 M trimethylanilin-ium hydroxide in methanol, is, in principle, the same as that used for other pre-column derivatizations. However, with this system the reaction does not occnr immediately because insufficient activation energy is available at ambient temperature for this to take place. Direct transfer of the reaction mixture onto the heated injection block of the gas chromatograph overcomes this problem and the derivatization reaction can then proceed. Snch a reaction, an example of flash alkylation is illustrated in Scheme 9.1. 

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