The detection and structural characterization of the components of a mixture is a challenging task. Therefore, to develop a facile and general method that enables both the separation and the structural characterization of the components is desired. Researchers from Public Laboratory of Qingdao institute of Bioenergy and Bioprocess Technology (QIBEBT), Chinese Academy of Sciences (CAS) developed a general matrix for high-performance chromatographic Nuclear Magnetic Resonance (NMR) spectroscopy, making a progress in the mentioned research area.  

A general method is often implemented by the use of hyphenation of chromatography with spectroscopy for the identification of compounds in chromatographic eluents, for example, Gas Chromatograph-Mass Spectrometer (GC-MS), Liquid chromatography–mass spectrometry (HPLC-MS), or HPLC-NMR. In QIBEBT, associate professor HUANG Shaohua and his team developed diffusion-ordered NMR spectroscopy (DOSY) and dubbed chromatographic NMR spectroscopy. DOSY is able to separate the components of a mixture without the aid of chromatographic tools, and obtain the structural characterization of each component. Thus, it could decrease the time and lowing the cost of analysis. Pure DOSY, however, can tap its potential only by the use of virtual stationary phase (VSP) matrix.  

Dr. HUANG’s team has discovered a new versatile VSP, poly(dimethylsiloxane) (PDMS), which can fully separate many mixtures of different structural types by liquid-state NMR spectroscopy. PDMS is very simple in its structure, and only shows a single signal at a higher field in the NMR spectrum just as tetramethylsilane (TMS). The signal of PDMS overlaps with those of hardly any other compounds. 

Notably, the addition of PDMS does not significantly increase the viscosity of a solution in comparison with that of the pure solvent. Furthermore, PDMS is inexpensive. Therefore, PDMS is an essentially perfect VSP. Most importantly, PDMS demonstrates a remarkable capability to separate many mixtures of similar species. Overall, PDMS holds great potential for becoming a general VSP for Chromatographic NMR spectroscopy. For example, Figure 1 displays ¹H DOSY spectra of a mixture consisting of anthracene, naphthalene, and benzene. The measurements were performed in CDCl₃ in the absence or presence of PDMS. In the absence of PDMS, the three components exhibited almost the same diffusion coefficient value and were not separated in the diffusion dimension (Figure 1 left). In comparison, the three components were well-resolved in the presence of PDMS and could be readily assigned in the DOSY spectrum (Figure 1 right). 

Syntheses chemists can alternatively use the matrixed DOSY to monitor the process of various reactions and obtain the composition and structural characterization of each component. It is able to avoid much work of separation and purification. Moreover, analytical chemists can make use of the mentioned tool, without the aid of classical chromatographic tools, to separate complex mixture.  

This research was supported by the National Natural Science Foundation of China and was led by Dr. HUANG Shaohua from Open Laboratory, QIBEBT, CAS. 

Figure 1. 1H DOSY spectra (600 MHz) of a mixture containing anthracene (5 mg), naphthalene (5 mg), and benzene (5 mg) before (left) and after (right) adding PDMS (50 mg) in 0.6 mL CDCl3. In spectrum (right), the diffusion coefficients of anthracene, naphthalene, and benzene were indicated by dotted lines, respectively. (Image by Open Laboratory, QIBEBT)

Reference:  

Huang, S., Gao, J., Wu, R., Li, S. and Bai, Z. (2014), Polydimethylsiloxane: A General Matrix for High-Performance Chromatographic NMR Spectroscopy. Angew. Chem. Int. Ed.. doi: 10.1002/anie.201406967.  http://onlinelibrary.wiley.com/doi/10.1002/anie.201406967/abstract  

Contact: 

Dr. Shaohua Huang 
Email: huangsh(AT)qibebt.ac.cn 
Web: http://english.qibebt.cas.cn