Abstract
Standard gas is well known as a reference gas or gas mixtures used as comparative standard in the calibration of analytical instruments, and the generation is grouped into static methods with gas cylinder and dynamic ones with diffusion and permeation tubes. In the case of acetaldehyde gas generation with a conventional permeation tube, more than one month of continuous generation has not been reported because the concentration of generated acetaldehyde significantly decreases within one month. Authors developed a novel permeation tube of acetaldehyde which aimed the lengthening of stable generation. A continuous monitoring of the concentration of acetaldehyde in the mixture was performed under different dilution gases (nitrogen and air) and temperatures (10, 20 and 30°C) by DNPH-HPLC method. A comparison of permeation rates obtained from HPLC analysis and mass loss of permeation tubes was also conducted. The results indicated that the permeability of acetaldehyde in nitrogen gas was 2320 ± 2.98 ng min-1 (k=2) at 10°C, and 6719 ± 0.87 ng min-1 (k=2) at 20°C. At 10°C and 20°C, the permeability of acetaldehyde determined with a mass loss of a tube showed constant for 3 months within the level of uncertainty and agreed with that from HPLC, whereas significant decrease at 30°C. These values agreed with those in the case of air. Acetic acid was detected in the residual solution in inside of the tube, whose permeability was negligibly small and had no effect on the concentration of generated acetaldehyde. An accurate acetaldehyde standard gas can therefore be provided using this permeation tube for 3 months, longer than one month with a conventional method, under the conditions of 10°C and 20°C.
