吸着・加熱脱着分析におけるサンプリング前処理に関する検討

Abstract

For adsorption—thermal desorption analysis, three ways of gas sampling pretreatments: 1) two water impingers (“Two impingers”); 2) two water impingers and two empty impingers (“Four impingers”); 3) cooling dehumidifier with Ag column (“Cooling dehumidifier”), were compared using aliphatic organic chlorinated compounds, chlorobenzenes and chlorophenols. Since the gas pretreatment system combines gas—liquid contact, distribution of chemicals between air and water was examined by a tank analogy model employing water volume, gas volume and Henry's constant. The compounds, Henry's constant of which is relatively low (those distribute more to water than to air) such as chlorophenols can neither pass “Two impingers” nor “For impingers” efficiently, while can survive at a rate of 70 % through “Cooling humidifier”, because it does not use water. Those compounds, the water solubility of which is high, such as chloroform and dichloromethane did not pass “Four impingers” although the estimated Henry's constant is adequately large. That suggests Henry's constant estimation involves considerable error for those compounds. Pretreatment loss caused by condensation and adsorption is sensitively affected by the property and the condition of the pretreatment device, namely, tetrachlorobenzene and larger compounds were significantly lost in “Four impingers” and “Cooling dehumidifier”, while “Two impingers” can pass pentachlorobenzene efficiently. Adsorption—thermal desorption property was studied using Carbotrap C. If the suctioned gas volume is increased, the recovery loss did not show exponential decrease, but the thermal desorption chart became split two peaks, main and shoulder, and desorption velocity went slow. That suggests the chemicals has diffused into the inner of the adsorbent. For the sake of the optimization of adsorption—thermal desorption analysis, limitation of analyzed chemical to avoid instrumental memory, and sensitive detection to quick determination and down-sizing of sampled gas volume.