Extensive Evaluation of a Diffusion Denuder Technique for the Quantification of Atmospheric Stable and Radioactive Molecular Iodine

In this paper we present the evaluation and optimization of a new approach for the quantification of gaseous molecular iodine (I-2) for laboratory- and field-based studies and its novel application for the measurement of radioactive molecular iodine. alpha-Cyclodextrin (alpha-CD) in combination with 129I(-) is shown to be an effective denuder coating for the sampling of gaseous I-2 by the formation of an inclusion complex. The entrapped I-127(2) together with the I-129(-) spike in the coating is then released and derivatized to 4-iodo-N,N-dimethylaniline (4-I-DMA) for gas chromatography-mass spectrometry (GC-MS) analysis. The I-127(2) collected can be differentiated from the I-127(2) spike by MS. A set of parameters affecting the analytical performances of this approach, including amount of alpha-CD and 129I(-) applied, denuder length, sampling gas flow rate and sampling duration, relative humidity, sample storage period, and condition of release and derivatization of iodine, is extensively evaluated and optimized. The collection efficiency is larger than 98% and the limit of detection (LOU) obtained is 0.17 parts-per-trillion-by-volume (ppty) for a sampling duration of 30 min at 500 mL min(-1). Furthermore, the potential use of this protocol for the determination of radioactive I-2 at ultra trace level is also demonstrated when 129I(-) used in the coating is replaced by 127I(-) and a multiple denuder system is used. Using the present method we observed 25.7-108.6 pptv I-127(2) at Mweenish Bay, Ireland and 10(8) molecule m(-3) I-129(2) at Mainz, Germany.