Measurement of formic acid, acetic acid, formaldehyde and acetaldehyde in the atmosphere by ion chromatography

A method for the determination of formic acid, acetic acid, formaldehyde and acetaldehyde in the atmosphere by ion chromatography was investigated. These gases were collected by using two bubblers in series filled with 50 ml distilled water as a trapping solution. The collection efficiencies of the gases by this sampling system were almost 100% at an air flow rate 5 1/min for 4 h in the field measurement. Formic acid and acetic acid collected with distilled water were directly analyzed by ion chromatography. 0.005 M Na2B4O7 was suitable eluent for the ion chromatographic analysis of formate and acetate ions. It was possible to obtain good separation of formate and acetate ions and complete the analysis within 8 min by using 0.005 M Na₂B₄O₇ eluent. Formaldehyde and acetaldehyde collected with distilled water could not be directly determined by ion chromatography with a conductimetric detector. It is therefore necessary to oxidize these aldehydes in the sample solution to formate and acetate for ion chromatographic analysis. The complete oxidation of formaldehyde and acetaldehyde to formate and acetate could be achieved by adding 5 ml of 1% H₂O₂ and 5 ml of 1 M NH₄OH to a 40 ml sample solution, no loss of formate and acetate by the addition was observed. The concentration column was used for the analysis of samples at lower concentration levels. The relative standard deviations of 0.5 ppm formate and acetate determinations by the concentration column were 3~5%, and the detection limits were 0.005 ppm for formate and 0.01 ppm for acetate for a 5 ml injection volume. The measurements of the above gases in the atmosphere were done at two locations (Hiyoshi, Yokohama and Shiroganedai, Tokyo, from April to December, 1985) by using this method. The concentration range was l.5~7.5 μg/m³ for formic acid, 18.8~35.3 μg/m³ for acetic acid, 2.9~18 μg/m³ for formaldehyde and 5.3~ 18.8 μg/m³ for acetaldehyde, respectively. For a 1.2 m³ air sampling volume, the detection limits of this method were 0.2 μg/m³ for formic acid and formaldehyde and 0.4μg/m³ for acetic acid and acetaldehyde.