Effect of Adsorbed Water on Solvent Desorption of Organic Vapors Collected on Activated Carbon

Abstract

Two activated carbons with the same surface area and pore volume, Merck (pH in aqueous solution 5.7) and SKC (pH 9.7), have been used. Desorption studies with carbon disulfide showed that for nonpolar compounds – such as toluene and 1,1,1-trichloroethane – recoveries were not affected by preadsorbed water. The addition of 2 µL water/100 mg carbon resulted for dioxane and butanol in an increase in recovery for Merck carbon and a decrease for SKC carbon. Twenty microliters of water (corresponding to a relative humidity of approximately 80%) caused a drop in recovery in proportion to the distribution ratio water/carbon disulfide. The decrease in recovery was in the order ethyl cellosolve>butanol>dioxane. The results could be explained partly by phase-separation, but water also appears to change the adsorptive properties of the carbon surface. The use of dimethyl formamide, a solvent capable of dissolving water, was found to be efficient in removal of analyte in presence of water. Desorption isotherms in the range 0.2–10 µL sample could be well fitted to a Freundlich isotherm.