Abstract
The Henry’s law constant (KH; M atm-1) plays an important role on the study of the distribution and the fate of chemicals in the environment. In principle ammonium ion (NH4+) becomes gaseous ammonia (NH3(g)) in aqueous solutions at alkaline environment. The Henry’s law constant of ammonia in 1 M sodium hydroxide (NaOH) over a temperature range of 283□323 K can be precisely determined using a homemade purge-and-trap system with ion chromatography and o-phthaldialdehyde (OPA) derivatization fluorescence as analysis method. The results were also compared with KH previously measured in 0.1 and 10 M NaOH and showed that the values of KH of ammonia decreased with increased ionic strengths of solution as a result of salting-out effect. The corrected experimental KH in deionized water was 50 M atm-1 at 298 K and 19 M atm-1 at 313 K by using Setschenow equation. The relation of KH with temperature was described by the equation: log KH= -6.36+2352.7/T, T= 283□323K. This system could also be applied to measure KH of C2-C9 primary amines simultaneously by using OPA derivatization HPLC with fluorescence detection.