Evaluation Of Detection Efficiency Of Dielectric Barrier Discharge Ionization Mass Spectrometry And Exploration Of Its Practical Application

Dielectric barrier discharge ionization(DBDI)is an atmospheric pressure ionization technology in which an alternating voltage is applied between two electrodes separated by a dielectric to generate plasma to ionize the analyte.In recent years,it has been widely studied and applied by virtue of high ionization efficiency,low energy consumption,and portability.In this paper,we used a new type of active capillary DBDI source,coupled with the laboratory’s existing commercial time-of-flight mass spectrometry(TOF-MS)which with an atmospheric pressure interface.The detection efficiency of the DBDI-MS device was evaluated.Then,a YAG 532 nm solid-state pulsed laser was introduced,and an atmospheric pressure laser desorption dielectric barrier discharge ionization mass spectrometer(LD-DBDI-MS)was built for practical application analysis.The contents of this thesis are:1.We used a self-built pressure-assisted nanospray thermal-evaporation device to quantitatively volatilize liquid sample and coupled it with the dielectric barrier discharge ionization mass spectrometry.The Poiseuille formula was used to obtain the flow rate of the sample.Three model molecules:tricyclazole,imazalil,and pyrimethamine were used to verify the detection capability ofthe device.This device had high sensitivity,and the limits of detection for gaseous samples were as low as ppt.Known the flow rates of the analyte and mass spectrometer injection,and then calculated the injection volume of the analyte per unit time of the DBDI-MS device,and calculated the ratio of the number of the analyte by the mass spectrometer per unit time to the number of molecules entering the DBDI per unit time,the detection efficiency of the entire DBDI-MS was about 2×10-6,which included the DBDI ionization efficiency,the quadrupole transmission efficiency,and the microchannel plate(MCP)detection efficiency.The establishment of this method provides a universal method for the evaluation of the detection efficiency of mass spectrometry.2.An atmospheric pressure laser desorption dielectric barrier discharge ionization mass spectrometry(LD-DBDI-MS)was built.With the high ionization efficiency and soft ionization characteristics of the DBDI,the device detection sensitivity was significantly improved.LDDBDI-MS was used for qualitative and quantitative detection of trace pesticide residues in complex matrix such as apple peel and soil sample.The standard quantitative curves of pesticide residues in apple peel and soil sample were established by standard addition method.Among them,the absolute limit of detection(ALOD)for the tricyclazole in apple peel,was as low as 1 ng,which is equivalent to 130 μg of tricyclazole kg-1 of apple.The detection result was far lower than the maximum residue limit(MRL)of tricyclazole in fruits and vegetables(2 mg/kg)specified in the China National Standard GB 2763-2019.This method has high sensitivity and good stability.Then another atmospheric pressure mass spectrometer API-TOF was used to detect tricyclazole and imazalil in soil sample using the same method.The limits of detection were as low as 5 ppm and 2 ppm,respectively.This method does not require sample pretreatment,and the detection of a single sample could be completed within 1 minute.LDDBDI-MS is expected to become a pre-screening tool for excessive pesticide residues in complex matrix such as fruit and soil.3.We used LD-DBDI-MS to quickly and semi-quantitatively detect nicotinamide in cosmetics,and established a standard quantitative curve of nicotinamide standard.The nicotinamide in cosmetics was extracted by simple demulsification and other pretreatment methods,then the mass spectrogram was obtained by LD-DBDI-MS.Then calculated the actual content of nicotinamide in the products by comparing their mass spectral signal strength with the standard curve.Among them,the nicotinamide content of Olay basically met the official label,but nicotinamide in the other product was far from the official label.Then we took pigskin as a real sample to simulate the penetration of nicotinamide in the skin,and through the tape bonding method and cryosection method combined with laser in-situ tissue sampling technology to depth profile analysis the transdermal absorption process of nicotinamide in the skin.This method provided references for researching on the mechanism of action of whitening products,product development and product safe use.