Quantitative Determination of Band Distortions in Diamond Attenuated Total Reflectance Infrared Spectra
Quantitative Determination of Band Distortions in Diamond Attenuated Total Reflectance Infrared Spectra
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DOI：
10.1021/jp101763y
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发表时间：
2010-06-24
影响因子：
3.3
通讯作者：
Pezolet, Michel
中科院分区：
文献类型：
--
作者：
Boulet-Audet, Maxime;Buffeteau, Thierry;Pezolet, Michel
由于其无与伦比的硬度和化学惰性，金刚石在极端条件和衰减全反射 (ATR) 红外光谱常规分析方面比其他材料具有许多优势。与锗相比，其低折射率可将吸光度提高多达 6 倍。不幸的是，与传输实验相比，它也会导致光谱失真较强的频带。本文的目的是提出一种定量确定 ATR 光谱中光谱畸变程度的方法。这种方法需要确定所研究样品的光学常数（折射率和消光系数）。作为一个典型的例子，蚕丝蛋白的光学常数是通过使用金刚石和锗内反射元件获得的偏振 ATR 光谱来确定的。锗和金刚石ATR发现的酰胺I带的位置分别比k(v)谱确定的真实值(计算出的1659 cm(-1))低6和17 cm(-1)。为了定量确定膜厚度和蛋白质浓度等相关参数的影响，还进行了各种光谱模拟。使用更薄的薄膜通过入射平面上的偏振光进行探测并稀释蛋白质样品可以帮助获得更接近其透射率对应物的 ATR 光谱。为了将这项研究扩展到任何系统，我们使用对不同强度和宽度的频带进行的光谱模拟来评估 ATR 失真幅度。从这些模拟中，我们发现了一个简单的经验关系，可以根据实验带高和带宽来估计带偏移，这对于 ATR 用户来说可能具有实际用途。本文表明，光学常数的确定提供了一种有效的方法来恢复失真 ATR 光谱的真实光谱形状和频带频率。
Due to its unmatched hardness and chemical inertia, diamond offers many advantages over other materials for extreme conditions and routine analysis by attenuated total reflection (ATR) infrared spectroscopy. Its low refractive index can offer up to a 6-fold absorbance increase compared to germanium. Unfortunately, it also results for strong bands in spectral distortions compared to transmission experiments. The aim of this paper is to present a methodological approach to determine quantitatively the degree of the spectral distortions in ATR spectra. This approach requires the determination of the optical constants (refractive index and extinction coefficient) of the investigated sample. As a typical example, the optical constants of the fibroin protein of the silk worm Bombyx mori have been determined from the polarized ATR spectra obtained using both diamond and germanium internal reflection elements. The positions found for the amide I band by germanium and diamond ATR are respectively 6 and 17 cm(-1) lower than the true value dtermined from the k(v) spectrum, which is calculated to be 1659 cm(-1). To determine quantitatively the effect of relevant parameters such as the film thickness and the protein concentration, various spectral simulations have also been performed. The use of a thinner film probed by light polarized in the plane of incidence and diluting the protein sample can help in obtaining ATR spectra that are closer to their transmittance counterparts. To extend this study to any system, the ATR distortion amplitude has been evaluated using spectral simulations performed for bands of various intensities and widths. From these simulations, a simple empirical relationship has been found to estimate the band shift from the experimental band height and width that could be of practical use for ATR users. This paper shows that the determination of optical constants provides an efficient way to recover the true spectrum shape and band frequencies of distorted ATR spectra.