Adsorption of water vapour from humid air in carbon molecular sieves: Carbosieve S-III and Carboxens 569, 1000 and 1001

Abstract

The adsorption of water vapour in carbon molecular sieves (CMS) used to determine volatile organic compounds (VOCs) in air was investigated. The CMS mass in the trap was found not to affect the mass of retained water under conditions of incomplete saturation of the adsorbent bed with water. Thus, the restrictions commonly imposed on the CMS mass are not necessary. The usefulness of four different CMSs to sample large volumes of humid air was estimated. Carboxen 1000 exhibited the best performance. To assess the magnitude of CMS mass in the trap in dependence on the volume, the relative humidity and the temperature of the sample, the use of a novel parameter, called the water vapour interference factor, was suggested.

Capillary thermal desorption unit for near real-time analysis of VOCs at sub-trace levels. Application to the analysis of environmental air contamination and breath samples

“…The evaluation of a multibed trap without the presence of a CMS showed that some of the main components in breath samples (e.g., acetone, methanol, ethanol) cannot be adequately adsorbed when only graphitized carbons are present in the sorbent tube. Given that Carboxen 1000 saturates at larger volumes of water than other CMS [26], it would seem to be the best choice for the analysis of breath samples.…”

On-line multi-bed sorption trap for VOC analysis of large-volume vapor samples: injection plug width, effects of water vapor and sample decomposition

“…Graphitized carbons do not adsorb water [16 -18] unlike carbon molecular sieves (CMS), which whilst adsorbing high amounts of water are required for the adsorption of highly volatile compounds. Fastyn et al [19] have demonstrated that Carboxen 1000 is the best choice for CMS as it does not become watersaturated with volumes of up to 5 L and 95% relative humidity (RH). In a previous study [6], we evaluated the capacity of a multi-bed sorption trap, containing a CMS (Carboxen 1000) in 100% RH samples, to adsorb VOCs.…”

Experimental choices for the determination of carbonyl compounds in air

“…Helmig and Vierling [48] proposed that the amount of adsorbed water depends on the volume and relative humidity of air, temperature, and mass (and identity) of the sorbent. Fastyn et al [49] proposed that the magnitude of the CMS mass is restricted by the tube dimensions, especially in the case of multilayer traps, and the hydraulic resistance; hence they recommended the use of Carboxen 1000 as an optional CMS for sampling large volumes of humid air, instead of other comparable materials (e. g., Carbosieve S-III, Carboxen 569, or Carboxen 1001). In contrast, graphitized carbon blacks (GCB), characterized by their high hydrophobicity and low specific surface area without micro-pores, do not adsorb water; they are hence ideal for sampling in an extremely humid atmosphere [45 -46].…”

“…Multibed adsorption tubes can also employ a CMS as the strongest adsorbent in the last layer. However, contact with humid air can deteriorate the sampling efficiency by blocking the adsorbent surface; if this phenomenon occurs, it can lead to as large as a tenfold decrease in safe sampling volume [49]. Helmig and Vierling [48] proposed that the amount of adsorbed water depends on the volume and relative humidity of air, temperature, and mass (and identity) of the sorbent.…”

“…A CMS is designed for the enrichment of light hydrocarbons in the range of C 2 -C 5 and is often used in combination with weaker adsorbents for sampling [1,44,46]. Some CMSs (such as Carbosieve S-III and Carboxens) have already been widely used in the analysis of airborne organic contaminants [49]. Multibed adsorption tubes can also employ a CMS as the strongest adsorbent in the last layer.…”