Low temperature sampling techniques for the determination of less volatile compounds in gaseous mixtures

Abstract

The analysis of trace quantities of the less volatile polar compounds (H2O, NH3, HCN, amines, alcohols, esters etc.) is frequently seriously affected by dubious sampling procedures. In the present contribution two different sampling techniques at dry ice temperature (195 K) are described which both claim considerable and predictable efficacy. Depending on whether the matrices of the samples are still gaseous or condensable at 195 K and ambient pressure, a scrubbing technique may be used or condensation in the presence of a suitable solvent with subsequent evaporation of the matrix. Some solvents and solvent mixtures with FP<195 K are compiled. The normally disadvantageous low volatility can be exploited for enrichment. The scrubbing technique enables detection limits of ∼1 ppb(V/V) to be achieved, the condensation technique ∼1 ppm(m/m). Simple checking methods for both techniques are described. Thermodynamic considerations for ideal mixtures enable the calculation of upper limits for possible deviations. Examples are presented.