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A USER'S GUIDE TO ALDEHYDE ANALYSIS USING PFBHA DERIVATIZATION AND GC/ECD DETECTION: AVOIDING THE PITFALLS
Citation:
Munch, J W. A USER'S GUIDE TO ALDEHYDE ANALYSIS USING PFBHA DERIVATIZATION AND GC/ECD DETECTION: AVOIDING THE PITFALLS. Presented at Water Quality Technology Conference, San Diego, CA, November 1-5, 1998.
Description:
Aldehydes are of interest because they have been identified as by-products of drinking water disinfection, particularly ozonation. In order to monitor treatment practices, assess exposure to consumers, and control health risks that might be associated with this class of by-products, a reliable and sensitive monitoring method is required.
To develop a reliable and sensitive monitoring method suitable for the analysis of C1-C10 straight chain aldehydes, glyoxal, methyl glyoxal, benzaldehyde, cyclohexanone, and crotonaldehyde, in finished drinking water, raw source water, or water at any treatment stage. The method is based on derivatization of the carbonyl compounds to the corresponding pentafluorobenzyl oxime derivative using pentafluorobenzylhydroxyl amine (PFBHA) as the derivatization reagent. While various other investigators have reported on this technique over the last decade, there has not been consensus on the optimum conditions for the derivatization, the necessary QC practices to monitor method performance, or the appropriate sample collection and preservation techniques.
Carbonyl compounds can react with PFBHA in aqueous solution to form pentfluorobenzyl oxime derivatives. These derivatives can be easily extracted from water with organic solvents, and are especially amenable to GC/ECD analysis because of their volatility and sensitivity to electron capture detection. In this derivatization, two isomers (E and Z) are formed for most carbonyl compounds. The efficiency of the derivatization reaction is dependent on the reaction time, temperature, pH and amount of reagent used. The effect of each of these variables on the reaction of each method analyte, in terms of overall reaction efficiency, as well as the effects on the E/Z isomer ratio will be presented. Results show that in general there is not one set of reaction conditions that is optimum for all analytes, but conditions can be selected to achieve the best overall performance for the group. Because the efficiency of the reaction is dependent on several variables, it is extremely important to be able to control those conditions, and to use QC procedures, such as the use of surrogate analytes, to monitor the reaction.
An important factor in obtaining reliable data for contaminants in environmental samples is the ability to collect and ship a valid sample to the analytical laboratory. This is an especially important issue for the analysis of aldehydes, because they are known to be readily biodegradable. Sample collection and preservation steps will be addressed. These will include, 1) chemical stability of analytes in aqueous solution, 2) sample dechlorination, and 3) the use of a biocide to prevent the loss of analytes due to microbiological activity.