A methodological approach for complex mixture aqueous solution analysis by ATR-FTIR spectroscopy

To develop an in situ, nondestructive approach for simultaneously acquiring overall structural and intermolecular interaction information of multiple components in complex aqueous mixtures without sample separation.

In this paper, attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) was utilized to detect and analyze the juice and decoction (clinical application forms) of different processed products of a traditional Chinese medicine (TCM)-Rehmanniae Radix (Dihuang in Chinese). By the analysis of IR and the second derivative IR (SD-IR) spectra, the spectral structure information of water, organic acid, stachyose, glucose, galactose, fructose, manninotriose, amino acid and protein in the mixture system was extracted through non separation fingerprint characteristic.

A large number of in situ dynamic tracked IR spectra, obtained by ATR-FTIR and TimeBase software, were used to excavate the changes of absorption peak intensity (structural analysis) and diffusion velocity (time resolution) in the process of liquid adsorption-diffusion. The results indicated the coexistence of free hydroxyl groups, intermolecular hydrogen bonds, and intramolecular hydrogen bonds, analyzed by two-dimensional correlation infrared spectroscopy (2DCOS-IR), confirming their complex and dynamic hydrogen-bonding network structures. Furthermore, spectral analysis revealed interactions among the various active components in the mixtures, providing a microstructural basis for interpreting their holistic effects.

This study provided a theoretical basis for the efficacy and pharmacologic mechanism of different processed forms of TCM from the perspective of physical chemistry. Also, it discussed how to carry out nondestructive and in situ dynamic tracking of complex mixture aqueous solution system, and how to study the timeliness, synergy and interaction of samples.