Nitrogen Trichloride Detection in Indoor Pool Air using Proton Transfer Reaction Mass Spectrometry

The purpose of this study is to accurately identify the concentration of nitrogen trichloride (NCl₃) in indoor swimming pool environments using Proton Transfer Reaction Mass Spectrometry (PTR-MS). NCl₃, a chloramine compound that forms from the reaction of HOCl and NH₃. It is a disinfection by-product that has been correlated to increased cases of asthma in swimmers. The amount of NCl₃ produced is dependent on the number of swimmers, the amount of NH₃ / urea released, the air change rate of the building, the amount of sunlight, and the concentration of HOCl in the water. In this work known concentrations of NH₂Cl, NHCl₂, and NCl₃ were synthesized and stock solutions quantified by UV/VIS spectrometry. Stock solutions were then used to make test gas mixtures for determining the PTR-MS response factors for these compounds. Test gas mixtures were made by calculating gas phase concentrations from stock solution concentrations and the Henry’s Law coefficient of the chloramines. Preliminary results have confirmed the PTR-MS’s ability to measure NCl₃. The continuous PTR-MS measurement method would thus be valuable for better determining exposures of NCl₃ by swimmers and pool workers. Further research will include testing the PTR-MS in an indoor pool environment and determining the NCl₃ concentration in the air.