Quantitative aqueous attenuated total reflectance Fourier transform infrared spectroscopy : Part II. Integrated molar absorptivities of alkyl carboxylates |
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Authors: | Paul R. Pike Pamela A. Sworan Stephen E. Cabaniss |
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Affiliation: | Department of Chemistry, Kent State University, Kent, OH 44242 USA |
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Abstract: | A quantitative attenuated total reflectance Fourier transform infrared (ATR-FT-IR) spectroscopic method is developed for the analysis of total carboxylate concentration, [COO−], in aqueous solution. The short (12–13 μm) and highly reproducible pathlength of the ATR cell permits quantitative subtraction of the water peak at 1640 cm−1. Carboxylate quantitation is based on the area of the asymmetric stretching peak, which is nearly independent of compound structure. The molar absorptivity of alkyl carboxylates in water is 438 ± 58 l mol−1 cm−1, and the integrated molar absorptivity is 2.95 ± 0.08 × 104 l mol−1 cm−2 (n = 15 compounds, 0.1 M ≤ [COO−] ≤ 1.5 M). The [COO−] in solutions of mixed carboxylates is measured with a root mean square error of 2.4% and a small (+1.5) positive bias. The accuracy of the method is limited by the assumption that integrated absorbance is constant for all COO− groups. |
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Keywords: | Infrared spectrometry Alkyl carboxylates Aqueous solutions Quantitative analysis |
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