Fundamental Factors in Detecting Chemicals as Adsorbed Films

摘要

Detection of trace chemicals in the atmosphere is possible by adsorption methods either through the results of physical adsorption or chemisorption processes. If the sensitivity of any such process is to be pushed to the limit, the ability to detect reliably the presence of a condensed monolayer or less becomes essential. Therefore, some of the general characteristics of surfaces and adsorbed monolayers deserve review with emphasis on the causes of the formation of the film and the conditions leading to optimizing the adsorption, the orientation, and the packing of the molecules to be detected. The nature of the forces responsible for adsorption are reviewed briefly and related to the reversibility of the adsorption process and to the average lifetime of adsorption. Cooperative adsorption including surface micellization, or cluster formation, mixed films, and the helpful or limiting effects due to the presence of previously adsorbed materials are discussed. Finally, some of the most sensitive methods of detecting and measuring the amount of adsorbed material will be reviewed with emphasis on their application to detection of chemicals in the atmosphere. (Author)