Zhigui Zhou

Recent advances of chromatography and mass spectrometry in lipidomics

Lipidomics, as a novel branch of metabolomics, which is aimed at comprehensive analysis of lipids and their biological roles with respect to health and diseases, has attracted increased attention from biological and analytical scientists. As a result of the complexity and diversity of lipids, accurate identification and efficient separation are required for lipidomics analysis. Mass spectrometry (MS) and chromatography have been extensively developed in the past few decades and hold a distinguished position in qualification and separation science. They are powerful and indispensable tools for lipidomics. Herein, we present the recent advancement of MS, chromatography, and their hyphenation technologies in lipidomics.

Thin layer chromatography/plasma assisted multiwavelength laser desorption ionization mass spectrometry for facile separation and selective identification of low molecular weight compounds.

A novel plasma assisted multiwavelength (1064, 532, and 355 nm) laser desorption ionization mass spectrometry (PAMLDI-MS) system was fabricated and applied in the analysis of low molecular weight compounds through combination with thin layer chromatography (TLC). The TLC/PAMLDI-MS system successfully integrated TLC, the multiwavelength laser ablation, and the excitated state plasma from direct analysis in real time (DART) and was proved to be effective in the facile separation and selective identification of low molecular weight compounds. An automated three-dimensional platform was utilized to facilitate the analysis procedures with all the parameters of the TLC/PAMLDI-MS systematically optimized, and the desorption/ionization mechanisms were discussed. The successful combination of three-wavelength laser with DART based system extended the range of the analytes and provided broad possibilities for the compound desorption from the TLC. The experimental results clearly showed that the laser desorption was wavelength dependent. The PAMLDI-MS system was successfully applied in the detection of low molecular weight compounds from different kinds of samples separated on a normal-phase silica gel, such as dye mixtures, drug standards, and tea extract, with the detection level of 5 ng/mm(2).

Rapid screening for synthetic antidiabetic drug adulteration in herbal dietary supplements using direct analysis in real time mass spectrometry

Adulteration of herbal supplements with synthetic drugs is illegal. A rapid and reliable method which utilizes direct analysis in real time mass spectrometry (DART-MS) was developed for the identification of seven synthetic antidiabetic drugs used as adulterants in herbal dietary supplements. The supplement sample was simply extracted with methanol/water by manually shaking several times and directly analyzed using DART-MS. The presence of synthetic drug adulterants was confirmed through the accurate m/z values and MS/MS data obtained via quadruple time of flight mass spectrometry (QTOF MS). Parameters for the DART source were systematically optimized, and the limits of detection (LODs) in herbal supplement matrices were measured. This method was successfully applied to examine five commercial herbal dietary supplements, and two of them proved to be adulterated with metformin without labeling.

Graphite-Coated Paper as Substrate for High Sensitivity Analysis in Ambient Surface-Assisted Laser Desorption/Ionization Mass Spectrometry

In this work, an extremely simple and quite sensitive mass spectrometric method termed ambient surface-assisted laser desorption/ionization mass spectrometry (ambient SALDI-MS) was developed to analyze different kinds of compounds, just using a piece of graphite-coated paper for the sample introduction. This provides great advantage in simplifying the analysis process. The method is quite easy to use, and there is no need to worry about the source of graphite, that is, the brands or the types of pencil. And the whole process was carried out under atmospheric pressure, offering all the merits that could occur in ambient MS. The improved sensitivity of this method is mainly because of the graphite, which serves as energy-transfer medium to absorb the energy of the photons and release it to the analytes that are adsorbed on the graphite surface. Also, three different laser wavelengths (1064, 532, and 355 nm) was tested to investigate the desorption mechanism. Fifty-one compounds, with varied chemical structures, were tried to prove that this new method possessed universal applicability to detect different kinds of small organic molecules.

Normal phase LC coupled with direct analysis in real time MS for the chiral analysis of 4‐(methylnitrosamino)‐1‐(3‐pyridyl)‐1‐butanol and jasmonic acid

Normal phase chiral LC (NPLC) has been proved to be powerful and efficient for chiral separation. However, the combination of NPLC with ESI or atmospheric pressure chemical ionization MS is restricted by the poor ionization efficiency and thermal fragmentations of analytes to some extent. Direct analysis in real time MS (DART‐MS) is an ambient ionization technique that shows high ionization efficiency of the analytes in the normal phase mobile phase. In this work, we coupled chiral NPLC to DART‐MS for the chiral qualitative and quantitative analysis of 4‐(methylnitrosamino)‐1‐(3‐pyridyl)‐1‐butanol and jasmonic acid enantiomers. Satisfactory results for the enantiomers of 4‐(methylnitrosamino)‐1‐(3‐pyridyl)‐1‐butanol operating in the positive mode were obtained in terms of linearity (2.5–250 μg/mL, R2, 0.999–1.000) and repeatability (25 μg/mL, RSDs, 4.7–5.6%). Moreover, chiral NPLC‐DART‐MS resulted in the simultaneous chiral separation and detection of jasmonic acid enantiomers, which are very difficult to be analyzed by NPLC‐ESI‐MS and NPLC‐APCI‐MS. Compared with the coupled techniques of NPLC‐ESI‐MS and NPLC‐APCI‐MS, NPLC‐DART‐MS showed advantages in increasing the ionization efficiency and reducing the in‐source thermal fragmentation of analytes.

Simultaneous determination of jasmonic acid epimers as phytohormones by chiral liquid chromatography–quadrupole time-of-flight mass spectrometry and their epimerization study

Jasmonic acid (JA) is an essential plant hormone involved in plant development and defense system. There are four stereoisomeric forms of JA and they act quite differently in vivo. In this work, a normal phase liquid chromatography-quadrupole time-of-flight mass spectrometry (NPLC-QTOF-MS) method using cellulose tris (4-methylbenzoate) coated silica gel as the chiral stationary phase was first established for the simultaneous discrimination and direct analysis of all the four JA stereoisomers without need of derivatization. A non-endogenous JA stereoisomer was introduced as the internal standard to ensure the reliability of the developed method. Satisfactory results were obtained in terms of sensitivity (limit of detection, 0.5 ng mL(-1) or 2.4 fmol), linearity (R(2)=0.9996) and repeatability (run-to-run RSD of migration time and peak area, 0.37% and 5.9%, respectively, n=6). Endogenous rise of two natural JA stereoisomers was detected in tobacco leaves and their variations in response to mechanical wounding were monitored. In addition, the configurational stability of JA stereoisomers was investigated using the stereoisomerically pure forms which were not commercially available but easily obtained by our semi-preparative chiral LC method. Experimental evidence indicated that both of the two naturally existing JA stereoisomers were putative signals for wounding response, and the epimerization between them was not a spontaneous process simply promoted by the thermodynamical instability as expected before.

Membrane-Based Continuous Remover of Trifluoroacetic Acid in Mobile Phase for LC-ESI-MS Analysis of Small Molecules and Proteins

We developed a “continuous” trifluoroacetic acid (TFA) remover based on electrodialysis with bipolar membrane for online coupling of liquid chromatography (LC) and electrospray ionization mass spectrometry (ESI-MS) using TFA containing mobile phase. With the TFA remover as an interface, the TFA anion in the mobile phase was removed based on electrodialysis mechanism, and meanwhile, the anion exchange membrane was self-regenerated by the hydroxide ions produced by the bipolar membrane. So the remover could continuously work without any additional regeneration process. The established LC-TFA remover-MS system has been successfully applied for the qualitative and quantitative analysis of small molecules as well as proteins.