基于溶液温度差谱分析的ATR-FTIR原位测量方法

作为一种原位、快速、无损坏的中红外光谱分析技术,ATR-FTIR已在很多工程领域得到越来越多的应用,尤其是针对结晶过程溶液浓度的原位实时测量。水是一种常用的结晶溶剂,在中红外波段具有强吸收峰,并且在不同温度下具有光谱吸收差异性,因而不能忽略溶剂水和温度对溶液浓度的中红外光谱测量带来的影响。以朗伯-比尔定律为基础,提出采用溶液光谱减去相应温度下的溶剂光谱的方法,从而能准确地测量溶液浓度。以L-谷氨酸溶液结晶过程为例,对L-谷氨酸水溶液的原始光谱数据、溶液光谱扣除常温(25℃)溶剂水的光谱数据以及溶液光谱对应温度扣除溶剂水的光谱数据分别进行建模。结果表明,提出的对应温度差谱法能有效消除溶剂水峰对溶质光谱测量的干扰,明显地降低了溶液浓度光谱标定模型的预测误差。该方法对提高原位ATR-FTIR光谱检测精度的实际应用具有一定的参考价值。

In-situ ATR-FTIR Measurement of Solution Concentration Based on Temperature-Related Spectra Difference Analysis

As an in-situ,fast and noninvasive mid-infrared spectroscopy technology,ATR-FTIR has been increasingly applied in many engineering fields,particularly in in-situ real-time measurement of the solution concentration during a crystallization process.Water is a common solvent for crystallization,which has very strong absorption peaks in the mid-infrared range but has different spectra absorbances under different temperature.Thus,the affects from water and its temperature could not be ignored in measuring the solution concentration in the mid-infrared range.Based on the Lambert-Beer's law,it is proposed in this paper to subtract the pure solvent spectra from the solution spectra under the same temperature to accurately measure the solution con-centration.Take the L-glutamic acid (LGA)solution as a case for illustration.Three calibration models were established for comparison by using the original spectra of LGA aqueous solution,the original spectra deducted uniformly by the water spectra under room temperature (25 ℃),and the solution spectra deducted by the water spectra and measured under the same tempera-ture,respectively.The results demonstrated that the proposed temperature-related differential spectra measurement method could effectively eliminate the influence of solvent on the spectra.The proposed method has a referential value for improving in-situ ATR-FTIR spectra measurement accuracy in practice.