Near-UV molar absorptivities of alachlor, mecroprop-p, pendimethalin, propanil and trifluralin in methanol

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 ɛ of five herbicides (alachlor, mecoprop-p, pendimethalin, propanil and trifluralin) in methanol. The absorption spectra were measured using a deuterium lamp at room temperature (298 ± 2 K) over the wavelength range 240–340 nm, except for pendimethalin and trifluralin where the wavelength range was extended to 240–550 nm.Absorbances were also measured at 253.7 nm using an Hg-lamp in different concentrations range depending on the studied compound. Except for mecoprop-p where absorbances were too low at this wavelength, the absolute values of molar absorptivity coefficients at 253.7 nm were determined according to the Beer–Lambert's law: ɛ = 381 ± 28 for alachlor, ɛ = 11,240 ± 1030 for pendimethalin, ɛ = 22,220 ± 1850 for propanil and ɛ = 5720 ± 410 for trifluralin (in units of M−1 cm−1). The quoted errors correspond to 2σ 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.