Environmental Monitoring of Volatile Organic Compounds Using Silica Gel, Zeolite and Activated Charcoal
- PDF / 1,009,121 Bytes
- 22 Pages / 612 x 792 pts (letter) Page_size
- 68 Downloads / 162 Views
Environmental Monitoring of Volatile Organic Compounds Using Silica Gel, Zeolite and Activated Charcoal Molly McGath1, Blythe McCarthy2, Jenifer Bosworth2 1
Heritage Science for Conservation, Department of Conservation and Preservation, Johns Hopkins University, Baltimore, MD 21218 USA 2 Freer Gallery of Art and Arthur M. Sackler Gallery, Smithsonian Institution, Washington, DC 20013 USA ABSTRACT Volatile organic compounds (VOCs) can be hazardous to human health and can negatively impact the long-term stability of art objects. This research evaluated the VOC adsorbent properties of three materials commonly used in museums as humidity regulating or air filtering agents. Silica gel, activated charcoal, and zeolite powder, materials often placed in proximity to art objects, were analyzed using Thermal Desorption GC-MS to qualitatively identify adsorbed VOC’s from model environments. This research compared the adsorbing capabilities of these materials with a solid-phase micro-extraction (SPME) carboxen/polydimethyl siloxane fiber to frame their adsorbing powers. It was found that different adsorbents have very different ranges of adsorption for the chemicals tested. Silica gel powder and zeolite powder have the greatest sensitivity for acetic acid over a 24 hour exposure period. Zeolite powder and activated charcoal were more sensitive for identification of naphthalene. Silica gel powder proved to be the most sensitive adsorbent overall. This research discovered that the methods used to condition silica gel pellets for reuse need to be re-examined in light of fact they trap VOC’s, especially as it was observed that VOC’s desorb from the silica gel pellets under ambient conditions. INTRODUCTION Volatile organic compounds (VOCs) are hydrocarbon rich chemicals with varying functionalities that typically have low boiling points and high vapor pressures. Some materials release VOCs over time, and in some cases this is a planned release of VOCs in a drying/curing step as seen with paint or caulking. In other cases the VOCs are given off over the life-span of the material, either as compounds that migrate out of the material: as is seen with plasticizers in some plastics [1]; or as the material ages or breaks down: as is seen in the aging and degradation of wood [2], wool and other proteinaceous materials [3], or in food as it spoils [4] [5]. Monitoring VOCs provides information on the presence of chemicals which can be hazardous to both humans [6][7][8] and art [9] [2] [1]. As VOCs enter the air they are diluted, often to concentrations below the limits of direct measurement. Some compounds, many sulfur containing, present observable odors at low ppb concentrations [10]. Some compounds are health hazards even at low concentrations [8]. VOC damage to art has been seen in the darkening of lead white by exposure to sulfur-containing compounds that migrate out of materials[11], and the tarnishing of silver objects to highlight just a few instances [12]. Acetic and formic acids, which are the breakdown products of wood [13],
ar
Data Loading...
