Brendan G. DeLacy, Science Applications International Corporation (SAIC), 201 Secretariat Drive Unit D, Havre de Grace, MD 21078 and Alan R. Bandy, Drexel University, Department of Chemistry, 3141 Chestnut Street, Philadelphia, PA 19104.
An atmospheric pressure ionization mass spectrometry/isotopically labeled standard (APIMS/ILS) method has been developed for the determination of carbon dioxide concentration and flux in the atmosphere. Method development involved the optimization of ion optics, ionization chemistry, and detection system. The APIMS/ILS method provides both an alternative and advantages over the currently used non-dispersive infrared (NDIR) technique. In addition to the description of the APIMS/ILS method, errors in carbon dioxide concentration measurements that are introduced by dryers are discussed. Many methods including the NDIR and APIMS/ILS techniques require a dryer to enhance the sensitivity. However, this drying process produces errors in techniques that measure molar concentration. An equation derived from the Ideal Gas Law, the conservation of mass, and Dalton’s Law describes and quantifies these errors. Laboratory experiments were conducted to verify the errors created by the dryer. The errors observed in these experiments verified the theoretical errors predicted in the derived equations. It should be noted that the APIMS/ILS method is not subject to the errors associated with drying, since mixing ratios are measured rather than molar concentration.