Central Laser Facility, RCaH, STFC Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, DidcotOX11 0QX, U.K.
Anal Chem. 2022 Dec 27;94(51):17988-17999. doi: 10.1021/acs.analchem.2c04287. Epub 2022 Dec 14.
A spectrophotometric method for determining relative concentrations of infrared (IR)-active analytes with unknown concentration and unknown molar absorption coefficient is explored. This type of method may be useful for the characterization of complex/heterogeneous liquids or solids, the study of transient species, and for other scenarios where it might be difficult to gain concentration information by other means. Concentration ratios of two species are obtained from their IR absorption and two-dimensional (2D)-IR diagonal bleach signals using simple ratiometric calculations. A simple calculation framework for deriving concentration ratios from spectral data is developed, extended to IR-pump-probe signals, and applied to the calculation of transition dipole ratios. Corrections to account for the attenuation of the 2D-IR signal caused by population relaxation, spectral overlap, wavelength-dependent pump absorption, inhomogeneous broadening, and laser intensity variations are described. A simple formula for calculating the attenuation of the 2D-IR signal due to sample absorption is deduced and by comparison with 2D-IR signals at varying total sample absorbance found to be quantitatively accurate. 2D-IR and Fourier transform infrared spectroscopy of two carbonyl containing species acetone and -methyl-acetamide dissolved in DO are used to experimentally confirm the validity of the ratiometric calculations. Finally, to address ambiguities over units and scaling of 2D-IR signals, a physical unit of 2D-IR spectral amplitude in mOD/ is proposed.
一种用于确定具有未知浓度和未知摩尔吸光系数的红外（IR）活性分析物相对浓度的分光光度法进行了探讨。这种方法可能对复杂/不均匀液体或固体的特性研究、瞬态物种的研究以及其他可能难以通过其他手段获得浓度信息的情况有用。通过简单的比计算，从它们的 IR 吸收和二维（2D）-IR 对角漂白信号获得两种物质的浓度比。开发了一种从光谱数据推导浓度比的简单计算框架，将其扩展到 IR-泵浦-探测信号，并应用于跃迁偶极子比的计算。描述了用于校正由于种群弛豫、光谱重叠、波长相关泵吸收、非均匀展宽和激光强度变化引起的 2D-IR 信号衰减的校正。推导出了一个简单的公式来计算由于样品吸收引起的 2D-IR 信号衰减，并通过与不同总样品吸光度下的 2D-IR 信号进行比较，发现该公式在定量上是准确的。通过在 DO 中溶解的两种含有羰基的物质丙酮和-甲基-乙酰胺的 2D-IR 和傅里叶变换红外光谱实验证实了比计算的有效性。最后，为了解决 2D-IR 信号的单位和比例的模糊性，提出了一个 2D-IR 光谱幅度的物理单位为 mOD/。
