UV absorption spectrum and Henryʹs law constant of EPTC

Both UV–visible absorption spectrum and Henryʹs law constants H of S-ethyl dipropylthiocarbamate (EPTC) were investigated in this work. Absolute values of molar absorptivity coefficients of EPTC in methanol were determined using a deuterium lamp over the wavelength range 233–343 nm at room temperature (298 ± 2 K). Absorbances were also measured at 253.7 nm using an Hg-lamp in the concentration range 10–426 mg L−1. The absolute value of at this wavelength, = 45 ± 4 M−1 cm−1, was then determined according to the Beer–Lambertʹs law. The quoted error corresponds to 2σ obtained from the least square fit analysis and includes an estimated systematic error of 5% due to the uncertainties in aqueous concentrations. The absorbances measured were lower than 1.2 and did not exhibit any deviation from the Beer–Lambertʹs law. Henryʹs law constants H of EPTC were determined over the temperature range 278–293 K with a dynamic system based on the existence of an equilibrium at the water/air interface within the length of a microporous tube. The obtained data were used to derive the following Vanʹt Hoff expression: ln H = (9134 ± 1180)/T − (26.6 ± 3.9) leading to a mean value of 91 ± 22 M atm−1 at 293 K. The quoted errors are given at 2σ level from the least-squares analysis and include the estimated systematic error of 5%. It is shown that, at a cumulus cloud temperature of 283 K, the fraction of EPTC in the atmospheric aqueous phase is negligible and therefore this compound will be mainly present in the gas phase.