Exploring lipid markers of the quality of coix seeds with different geographical origins using supercritical fluid chromatography mass spectrometry and chemometrics

Background: Lipids, a group of primary metabolites, could be used as quality markers of Traditional Chinese medicine.

Purpose: The present study was designed to develop a research method to explore lipid markers of the quality of coix seeds with different geographical origins.

Study design: The geographical origins of coix seeds were divided into three regions based on the latitude. A central composite design (CCD test) was used to optimize the chromatographic parameters of supercritical fluid chromatography to obtain optimal lipid profile of coix seed.

Methods: An untargeted method based on ultra-performance convergence chromatography - quadrupole/time-of-flight hybrid mass spectrometry (UPC²-QTOF) was developed. Four chromatographic parameters were optimized using CCD test, and a fusion index established by Derringer function was used to evaluate. The lipid profile of 27 batches of coix seeds were acquired and processed by Progenesis QI software, and the MS/MS spectrums were obtained to identify, simultaneously. The difference lipids were explored by orthogonal partial least squares discriminant analysis (OPLS-DA). The lipids that showed differences depending on their seeds' geographical origin were selected as markers of the quality of coix seeds from the three regions.

Results: A Torus 2-PIC (1.7 µm, 100 mm × 3.0 mm) was selected as the optimal column of the untargeted method which the run time was only 8 minutes. From the CCD test, the interaction of chromatographic parameters between column temperature and backpressure was founded which the optimal parameters were 55 °C and 2600 psi, respectively. Thirty-two peaks in the lipid profile of coix seed were tentatively identified, of which 20 were triglyceride, and 12 were diglyceride. Nine features that could potentially be used to distinguish the coix seeds by their geographical origin were identified, most of which were diglycerides, such as OP.

Conclusions: Our findings confirm that UPC²-QTOF combined with chemometrics could be used as an efficient method for exploring potential lipid markers of the quality of herbal medicine.