Application of two-dimensional chromatography in the analysis of Chinese herbal medicines

For the purpose of better understanding the complex Chinese herbal medicines (CHMs) and controlling their quality, powerful analytical techniques are essential. Although conventional one-dimensional (1D) chromatographic approaches have been widely used for the analysis of multiple components in CHMs, the complexity of CHM samples often exceeds the maximal capacity of any single separation mode. Therefore, in past decades, many researchers have attempted to explore the coupling of independent separation techniques to improve the resolving power for complex CHM samples. Two-dimensional (2D) separation systems, based on two independent columns with different separation mechanisms, have proven to be more powerful than 1D techniques and have been used successfully to separate and analyze CHM samples with excellent performance. This article aims to review the most recent advances in the strategies for analyzing CHMs using 2D chromatography. For this purpose, some remarkable applications of the commonly used couplings, mainly including 2D-GC and 2D-LC for analysis of CHMs, are described. Moreover, their major advantages and shortcomings are discussed, which might be helpful to the researchers who focus on quality control of CHMs.