Near-UV molar absorptivities of acetone, alachlor, metolachlor, diazinon and dichlorvos in aqueous solution

An experimental set-up consisting of two parallel absorption cells coupled to a CCD detector was used to determine absolute values of molar absorptivity coefficients epsilon of acetone and of several pesticides (alachlor, metolachlor, diazinon and dichlorvos) in water. The absorption spectra were measured using a deuterium lamp over the wavelength range of 240-320 nm at room temperature (298 +/- 2 K). Absorbance were also measured at 253.7 nm using an Hg-lamp in different concentrations range depending on the studied compound. The absolute values of molar absorptivity coefficients at this wavelength were determined according to the Beer-Lambert law: epsilon = 13.9 +/- 1.0 for acetone, epsilon = 466 +/- 41 for alachlor, epsilon = 615 +/- 63 for metolachlor, epsilon = 3558 +/- 323 for diazinon, epsilon = 5.5 +/- 0.5 for dichlorvos (in units of M-1 cm(-1)). The quoted errors correspond to 2 sigma obtained from the least square fit analysis and the estimated systematic error of 5% due to the uncertainties in aqueous concentrations. For all the studied compounds, the absorbances measured were lower than two and did not exhibit any deviation from the Beer-Lambert's law. (C) 2005 Elsevier B.V. All rights reserved.