Collection and analysis of organic acids in exhaust gas. Comparison of different methods

This paper reports the development of a specific method to identify organic acids in exhaust gases. The organic acids are collected in two impingers c ontaining liquids (pure water or Na2CO3 1% aqueous solution) and four cartr idges containing solids (silica, fluorisil, alumina B and alumina N). Once collected, the acids are eluted of the solids by a hot water stream. These traps performances, in terms of organic acids collection and elution effici ency, are evaluated and compared. Two sources are used to produce the gas f low containing organic acids: one generates a flow whose concentration is k nown and stable, the other produces organic acids among other combustion pr oducts. For eluted solutions analysis. two methods are used: isocratic ioni c chromatography/conductivity detection and GC/FID. Their efficiency in sep arating 10 aliphatic acids are compared. Their characteristics such as dete ction limits, detection linearity, repeatability and possible interferences with other components found in exhaust gases are determined. The stability of the organic acids solutions is also studied. Lastly, the use of these m ethods is illustrated by the analysis of the gas-phase organic acids exhaus ted by a spark ignition and by a diesel engine. (C) 1999 Elsevier Science L td. All rights reserved.