Jialing Zhang

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.

Study on Variation of Lipids during Different Growth Phases of Living Cyanobacteria Using Easy Ambient Sonic-Spray Ionization Mass Spectrometry

Lipids are important components of cell membranes and thylakoids in cyanobacteria, and they play vital roles in various biological activities. Real-time tracing of the variation of membrane lipids can provide insights of the physiological status of cyanobacterial cells. In this work, easy ambient sonic-spray ionization mass spectrometry (EASI-MS) was utilized to investigate the changes of acidic lipids in unicellular (Synechocystis 6803, Synechococcus 7002) and filamentous (Anabaena 7120) cyanobacteria during different growth phases. A sqdX mutant with a reduced synthesis of sulfoquinovosyl diacylglycerol (SQDG) was constructed to verify the acquired data of EASI-MS. Principal component analysis (PCA) was performed to compare the acquired data, enabling the discrimination of different species of cyanobacteria in day-to-day analysis. The results showed that the three representative cyanobacteria and their growth status can be easily determined on the basis of the lipids components detected by EASI-MS. Very interestingly, significant decreases of the ratios of SQDG/PG and dramatic changes of the unsaturation level of lipids were observed in different culture times in these cyanobacteria, and these two unique characters can be used describe the aging of cyanobacteria.

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.

New Strategy for Further Improving the Detection Sensitivity of Direct Analysis in Real Time-Mass Spectrometry

Ambient mass spectrometry facilitates surface detection under ambient conditions and has quickly found its applications in various areas. However, the sensitivity of AMS methods is usually not as good as that of encapsulated ion sources due to less efficient ion transmission. In this work, a briefly machined external ion funnel (three-pole electrostatic lens) was adopted and installed between direct analysis in real time and the mass spectrometer inlet to increase detection sensitivity. Software investigation with SIMION version 8.0 was employed to calculate electric fields and to simulate the trajectories of charged particles in the electric field. Both the geometrical parameters of the ion funnel and the electric parameters were studied to obtain the optimal ion focusing results, which demonstrated the ion funnel equipment would greatly improve the ion transmission efficiency. The equipment showed good prospect in direct analysis in real time-mass spectrometry analysis in the future.