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Photoinduced nucleation: a novel tool for detecting molecules in air at ultra-low concentrations

United States Patent

October 22, 2002
View the Complete Patent at the US Patent & Trademark Office
A method and apparatus for determining the presence of molecules in a gas at concentrations of less than about 100 ppb. Light having wavelengths in the range from about 200 nm to about 350 nm is used to illuminate a flowing sample of the gas causing the molecules if present to form clusters. A mixture of the illuminated gas and a vapor is cooled until the vapor is supersaturated so that there is a small rate of homogeneous nucleation. The supersaturated vapor condenses on the clusters thus causing the clusters to grow to a size sufficient to be counted by light scattering and then the clusters are counted.
Katz; Joseph L. (Baltimore, MD), Lihavainen; Heikki (Masala, FI), Rudek; Markus M. (Bruchkoebel, DE), Salter; Brian C. (New Market, MD)
(Washington, DC)
09/ 629,468
August 1, 2000
The United States Government has rights in this invention pursuant to a Grant DE-FGO2-95ER62004 between the U.S. Department of Energy (DOE) and The John Hopkins University