result from the lack of polarographic equipment in many laboratories. Gas chromatography and infrared spectroscopy certainly can be employed in analyzing for aldehydes in simplified systems lยฐ,11,~-xs, but are difficult to apply to aldehyde analysis in complex combustion effluents or the atmosphere.
METHODS OF ANALYSIS OF TOTAL ALDEHYDES
The method most widely used in practice to analyze for "aldehydes" is the bisulfite procedure19, 20. In this method an addition complex is formed between the aldehyde and the bisulfite compound, the excess bisulfite is destroyed, the addition compound decomposed, and the bisulfite ion released is titrated with standard iodine solution. Actually, both aldehydes and some ketones are determined by this method. Although formaldehyde, acetaldehyde and propionaldehyde may be efficiently collected and determined, it is generally more difficult to analyze quantitatively for ketones by this method 21,2~. While the method has sufficient sensitivity for combustion effluent analysis, the limit of sensitivity often is being pressed in using the method to determine concentrations in the tenths of a p.p.m, range in the atmosphere19, 2~.
All of the above factors tend to make the "aldehyde" concentrations determined by the bisulfite procedure somewhat uncertain. Obviously when large amounts of ketones exist in the combustion effluent or the atmosphere, the "aldehydes" determined will be higher than the true concentration of aldehydes. If significant amounts of ketones are present but the sampling is done at room temperatures or above, and at flow rates of 0.I c.f.m, or higher, then some losses of ketones and of C4 and higher aldehydes can result ~1. If only one or two impingers are used under these conditions even more serious losses may occur. Preferably, collection should be at about one liter per min into a series of three impingers placed in an ice bath. However, it also is possible that the degree of accuracy to be expected from the method in air pollution applications is insufficient to warrant all of the refinements mentioned. Whatever may be the limitations of this method, it is the only one which has been used in most investigations for aldehydes in combustion sources or in the atmosphere.
An argentimetric method using silver nitrate or silver oxide is quite specific for aldehydes, and it has some application for aldehyde analysis in combustion gases 4.~. The procedure, which involves titration of the silver salts with thiocyanate, is rather lengthy. The sensitivity is low, so the method is unlikely to be of any use in atmospheric analysis.
Another volumetric procedure which can be utilized involves oxidation of the aldehydes to the corresponding acids with hydrogen peroxide in alkaline medium TM. This method also is of limited sensitivity. It also may be applied to combustion gases but is of too low a sensitivity for atmospheric analysis.
An interesting polarographic method of aldehydes has been developed based on reduction of their semicarbazide derivatives ~4. Both aldehydes and ketones form such derivatives, but their half wave potentials are sufficiently different to permit a separate estimate of aldehydes and ketones. A small number of atmospheric measurements were made using this method. It might also be possible to determine the aldehydes directly in an appropriate electrolyte solution. Formaldehyde, a,fl-unsaturated aldehydes, and C2 and higher saturated aldehydes might be determined separately and then summed. Such a procedure should be applicable to combustion gases or other