Recently, high-throughput quantum cascade laser-based vibrational circular dichroism (QCL-VCD) technology has reduced the measurement time for high-quality vibrational circular dichroism spectra from hours to a few minutes. This study evaluates QCL-VCD for chiral monitoring using flow-through measurement of a changing sample in a circulating loop. A balanced detection QCL-VCD system was applied to the enantiomeric pair R/S-1,1'-bi-2-naphthol in solution. Different mixtures of the two components were used to simulate a racemization process, collecting spectral data at a time resolution of 6 min, and over three concentration levels. The goal of this experimental setup was to evaluate QCL-VCD in terms of both molar and enantiomeric excess (EE) sensitivity at a time resolution relevant to chiral monitoring in chemical processes. Subsequent chemometric evaluation by partial least squares regression revealed a cross-validated prediction accuracy of 2.8% EE with a robust prediction also for the test data set (error = 3.5% EE). In addition, the data set was also treated with the least absolute shrinkage and selection operator (LASSO), which also achieved a robust prediction. Due to the operating principle of LASSO, the obtained coefficients constituted a few discrete spectral frequencies, which represent the most variance. This information can be used in the future for dedicated QCL-based instrument design, gaining a higher time resolution without sacrificing predictive capabilities.

中文翻译：

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对映体过量和浓度空间的手性监测：利用量子级联激光器进行灵敏的振动圆二色光谱。

最近，基于高通量量子级联激光的振动圆二色性（QCL-VCD）技术已将高质量振动圆二色性光谱的测量时间从几小时缩短到几分钟。本研究使用循环回路中变化的样品的流通测量来评估 QCL-VCD 的手性监测。将平衡检测 QCL-VCD 系统应用于溶液中的对映体对 R/S-1,1'-bi-2-萘酚。使用两种组分的不同混合物来模拟外消旋过程，以 6 分钟的时间分辨率和超过三个浓度水平收集光谱数据。该实验装置的目标是在与化学过程中手性监测相关的时间分辨率下评估 QCL-VCD 的摩尔和对映体过量 (EE) 灵敏度。随后通过偏最小二乘回归进行的化学计量学评估显示，交叉验证的预测精度为 2.8% EE，测试数据集的预测也具有稳健性（误差 = 3.5% EE）。此外，还对数据集进行了最小绝对收缩和选择算子（LASSO）处理，同样实现了稳健的预测。由于LASSO的工作原理，所获得的系数构成了几个离散的谱频率，它们代表了最大的方差。这些信息将来可用于基于 QCL 的专用仪器设计，在不牺牲预测能力的情况下获得更高的时间分辨率。