Reduction number volatility

N-Nitrosamines, formed principally from the reaction of naturally occurring secondary amines with nitrites that may be added to foods or produced by bacterial reduction of nitrates, have been identified in many food systems including cured meat products, nonfat dried milk, dried malt and beer. In addition, the presence of less volatile and non-volatile N-nitroso compounds or their precursors in foods have been suggested from a number of model system studies. 

It was noticed as early as 1925 that alkoxides of calcium, magnesium and particularly aluminum could catalyze the reduction of aldehydes by ethanol as shown in equation (65).242,243 Removal of very volatile acetaldehyde is easily achieved to drive the reaction to the right. In 1926, Ponndorf devised a method in which both aldehydes and ketones could be reduced to alcohols by adding excess alcohol and aluminum isopropoxide.244 Such reductions are today referred to as Meerwein-Ponndorf-Verley reactions. Although alkoxides of a number of metals, e.g. sodium, boron, tin, titanium and zirconium, have been used for these reactions, those of aluminum are by far the best. 

A number of composition analyzers used for process monitoring and control require chemical conversion of one or more sample components preceding quantitative measurement. These reactions include formation of suspended solids for turbidimetric measurement, formation of colored materials for colorimetric detection, selective oxidation or reduction for electrochemical measurement, and formation of electrolytes for measurement by electrical conductance. Some nonvolatile materials may be separated and measured by gas chromatography after conversion to volatile derivatives. 

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