Aldehydes, Ketones, Alcohols, and. Carboxylic Acids

FIGURE 11.38 Average percent differences from the NIST standards for all participating laboratories ( ) and the percent standard deviation of all measurements ( ) (adapted from Apel et at., 1994). 

FIGURE 11.39 Results of intercomparison study of a mixture of organics found in ambient air. The concentrations (in ppbC) are shown as unfilled bare, along with the coefficient of variation ( ) for these measurements (adapted from Bernardo-Bricker et at., f995). 

In addition to the spectroscopic methods, there are a number of derivatization methods, in which a derivative of the carbonyl compound that can be easily separated and measured is formed. The most common of these is the use of 2,4-dinitrophenylhydrazine (DNPH), which reacts to form the hydrazone  

The mixture of hydrazones formed from the reactions of the set of carbonyl compounds commonly found in air can then be separated using HPLC and detected using light absorption at 254 or 365 nm (e.g., see Kuntz et al., 1980 Lipari and Swarin, 1982 and Kuwata et al., 1983). 

The aldehydes and ketones can be collected in several different ways. One of the most common is the use of solid sorbents such as silica gel, Florisil, or C,x cartridges that are coated with DNPH (e.g., see Lipari 

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Oxidations of hydrocarbons (cycloalkanes, cycloalkenes, aromatics) photo-catalyzed by metallotetrapyrroles lead to the formation of epoxides, aldehydes, ketones, alcohols, and carboxylic acids both in solutions and polymer matrices. These processes frequently occur as selective (one-product formation) reactions. Irradiation with visible light has a pronounced accelerating effect on such important industrial processes as the oxidation of thiols to disulfides (Merox process [265]) in a treatment of petroleum distillates or waste water cleaning. 

In summary, if an API has an aldehyde, ketone, alcohol, and/or carboxylic acid, be careful in developing a formulation (excipients and processing) and developing analytical procedures (sample preparation, mobile phase, and type of packaging chosen for stability studies) based on the specific examples presented in the above sections (aldehyde, ketone, alcohol, and carboxylic acid). 

The ether group in dmgs such as econazole nitrate (III) and miconazole nitrate (IV) is susceptible to oxidation. The process involves removal of hydrogen from the C-H bonds in the a-position to the oxygen to produce radicals, which further degrade to a-hydroperox-ides and evenmally to aldehydes, ketones, alcohols and carboxylic acids. 

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