scope:

Introduction

Aldehydes and ketones are a class of partially oxidized organic compounds which, owing to the reactive functional group, the carbonyl group, react rapidly at varying rates to form secondary products.

Short-chain aldehydes and ketones are formed in the incomplete combustion of hydrocarbons or alcohols, for example in firing plants or gasoline or diesel engines. The reactivity of aldehydes, particularly formaldehyde (methanal), is utilized industrially in the synthesis of some plastics. However, polymerization is not quantitative, so that aldehydes can escape during the curing phase.

Aldehydes and ketones are important ozone precursors and intermediates in the formation of "summer smog". In addition to their direct hazard to health [1] they are also hazardous to the environment via their degradation products. Thus, for example, peroxy and hydroperoxy free radicals, which can lead to high concentrations of photooxidants, in particular ozone, in chain-reaction systems, are among the secondary products of photochemical aldehyde breakdown [2].

The lower aldehydes are distinguished by a pungent aroma; even at very low concentrations they irritate the mucous membranes of the nose, eyes and respiratory pathways. For some components, MAK values [maximum permissible workplace concentration ¹)], which are published in the Technical Rules for Hazardous Substances (TRGS 900) [3] and for formaldehyde, the WHO specifies an air quality guideline value [4].

The emission of formaldehyde and acetaldehyde and of other aldehydes and ketones is limited under the German Technical Instructions on Air Quality Control - TA Luft [5].

Part 1 of guideline VDI 3862 [6] gives instructions on measuring short-chain aliphatic aldehydes by the MBTH method (3-methyl-2-benzothiazolinone hydrazone). The aldehydes are determined as a total. The sensitivity of response of MBTH to the individual aldehydes is variable. The method is suitable, in particular, for measuring formaldehyde emissions.

In Part 2 [7], a method is presented which enables aliphatic and aromatic aldehydes and ketones to be determined as individual components. The substances are reacted with 2,4-dinitrophenylhydrazine in the absorption solution (acetonitrile) in impingers to give the corresponding hydrazones and are quantified as individual components. The absorption solution is analyzed directly using high-performance liquid chromatography (HPLC).

In the present Part 3, a method is presented which enables the same aldehydes and ketones to be determined individually. The substances are reacted in cartridges with 2,4-dinitrophenylhydrazine (DNPH) on a solid sorption material to give the corresponding hydrazones. After elution with acetonitrile the individual components are analyzed using an HPLC instrument. Owing to the limited sorption capacity for aldehydes and ketones this method is predominantly suitable for measuring diluted exhaust gases or small amounts of samples.

¹) MAK values are published by the "Senatorial commission for the examination of hazardous working materials (Senatskommission zur Prüfung gesundheitsschädlicher Arbeitsstoffe)" of the German Science Foundation (DFG). The list of MAK values is annually checked and enlarged.