Quantitative aqueous attenuated total reflectance Fourier transform infrared spectroscopy: Part II. Integrated molar absorptivities of alkyl carboxylates
✍ Scribed by Paul R. Pike; Pamela A. Sworan; Stephen E. Cabaniss
- Publisher
- Elsevier Science
- Year
- 1993
- Tongue
- English
- Weight
- 718 KB
- Volume
- 280
- Category
- Article
- ISSN
- 0003-2670
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✦ Synopsis
A quantitative attenuated total reflectance Fourier transform infrared (AIR-IT-IR) spectroscopic method is developed for the analysis of total carboxylate concentration, [COO-], in aqueous solution. The short (12-13 pm) and highly reproducible pathlength of the ATR cell permits quantitative subtraction of the water peak at 1640 cm-'. 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 f 58 1 mol-' cm-r, and the integrated molar absorptivity is 2.95 f 0.08 X lo4 1 mol-' cm-* (n = 15 compounds, 0.1 M g [COO-] < 15 M). The [COO-] in solutions of mired 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.