Selective detection methods for gas chromatography of acetaldehyde and low molecular weight oxygen-containing compounds

For the measurement of gaseous compounds in air, a selective detection method(O-FID) for oxygen-containing compounds was developed. Two methods were examined: a catalytic dehydrogenation-methanation method {O-FID (CDM)}and a direct catalytic methanation method {O-FID(DCM)}. The O-FID(CDM) was based on (1) the catalytic decomposition of oxygen-containing compounds to CO and CO2 on reduced copper, (2) the conversion of CO and CO2 to methane in a stream of hydrogen on nickel and (3) the detection with FID. The O-FID(DCM) made use of (1) the direct catalytic formation of methane on reduced copper with a flow of hydrogen and (2) the measurement of methane with FID. In both cases, hydrocarbons were removed adsorptively with active carbon. Gas chromatography was carried out with Shimadzu GC-4BM equipped with Porapak Q packed glass cloumn(i. d. 3 mm, 2 m long) at 130°C isothermally. By O-FID (CDM), almost all oxygen-containing compounds studied were measured and their sensitivities were similar to those of the usual FID, while those of hydrocarbons by O-FID(CDM) dropped to 1/1000 to 1/10000 and about 200μg of hydrocarbons did not cause any interferences for gas chromatographic measurement of oxygen-containing compounds at sub-μg levels. As the results, it was found that O-FID(CDM) could be used for the selective analysis of most oxygen-containing compounds. On the other hand, the O-FID(DCM) was more specific to acetaldehyde and ethanol among low oxygen-containing compounds examined. The sensitivity of the O-FID(DCM) was almost the same as the usual FID for acetaldehyde which was quantitized down to 2 ng under the gas chromatographic conditions mentioned above without any interferences from hydrocarbons.