UV absorption spectrum and Henry's law constant of EPTC

Both UV-visible absorption spectrum and Henry's law constants H of S-ethyl clipropylthio-carbarnate (EPTC) were investigated in this work. Absolute values of molar absorptivity coefficients E 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 epsilon at this wavelength, epsilon=45 +/- 4 M(-1)cm(-1), was then determined according to the Beer-Lambert's law. The quoted error corresponds to 2 sigma 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-Lambert's law. Henry's 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 Van't Hoff expression: In 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 2 sigma 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. (C) 2008 Elsevier Ltd. All rights reserved.