Nonuniform Electric Field-Enhanced In-Source Declustering in High-Pressure Photoionization/Photoionization-Induced Chemical Ionization Mass Spectrometry for Operando Catalytic Reaction Monitoring

Abstract

Photoionization mass spectrometry (PI-MS) is a powerful and highly sensitive analytical technique for online monitoring of volatile organic compounds (VOCs). However, due to the large difference of PI cross sections for different compounds and the limitation of photon energy, the ability of lamp-based PI-MS for detection of compounds with low PI cross sections and high ionization energies (IEs) is insufficient. Although the ion production rate can be improved by elevating the ion source pressure, the problem of generating plenty of cluster ions, such as [MH]+·(H2O) n (n = 1 and 2) and [M2]+, needs be solved. In this work, we developed a new nonuniform electric field high-pressure photoionization/photoionization-induced chemical ionization (NEF-HPPI/PICI) source with the abilities of both HPPI and PICI, which was accomplished through ion–molecule reactions with high-intensity H3O+ reactant ions generated by photoelectron ionization (PEI) of water molecules. By establishing a nonuniform electric field in a three-zone ionization region to enhance in-source declustering and using 99.999% helium as the carrier gas, not only the formation of cluster ions was significantly diminished, but the ion transmission efficiency was also improved. Consequently, the main characteristic ion for each analyte both in HPPI and PICI occupied more than 80%, especially [HCOOH·H]+ with a yield ratio of 99.2% for formic acid. The analytical capacity of this system was demonstrated by operando monitoring the hydrocarbons and oxygenated VOC products during the methanol-to-olefins and methane conversion catalytic reaction processes, exhibiting wide potential applications in process monitoring, reaction mechanism research, and online quality control.

Hexapole-Assisted Continuous Atmospheric Pressure Interface for a High-Pressure Photoionization Miniature Ion Trap Mass Spectrometer

“…The evolution of intensity as a function of U hexapole – U skimmer is shown in Figure b, which revealed that a strong electric field between hexapole rods and the skimmer is beneficial for ion focusing. Similar results were also observed in another work . In the following experiments, the optimized RF and DC voltage was set to be 400 V pp and 7 V, respectively.…”

“…Similar results were also observed in another work. 39 In the following experiments, the optimized RF and DC voltage was set to be 400 V pp and 7 V, respectively.…”

Rapid Determination of Ethyl Carbamate in Chinese Liquor via a Direct Injection Mass Spectrometry with Time-Resolved Flash-Thermal-Vaporization and Acetone-Assisted High-Pressure Photoionization Strategy

“…The peak intensity of [EC + H] + rapidly increased when the acetone concentration increased from 0 to 200 ppmv, which was obviously attributed to production of more protonated acetone ions. The peak intensity of [EC + H] + then decreased when the acetone concentration was further increased from 200 to 1000 ppmv because more cluster ions [(C 3 H 6 O) n + H] + generated at higher concentrations of acetone and the reaction capacities for the reactions of [(C 3 H 6 O) n + H] + with EC molecules decreased. , Therefore, the optimal concentration of acetone was 200 ppmv. M false( analyte false) + h ν → normalM • + + normale − normalM • + + normalX → false[ normalM + normalH false] + + false[ normalX − normalH false] • C 3 H 6 O + h ν → normalC 3 normalH 6 normalO • + + normale − normalC 3 normalH 6 normalO • + + normalX → false[ normalC 3 normalH 6 normalO + normalH false] + …”

“…The peak intensity of [EC + H] + then decreased when the acetone concentration was further increased from 200 to 1000 ppmv because more cluster ions [(C 3 H 6 O) n + H] + generated at higher concentrations of acetone and the reaction capacities for the reactions of [(C 3 H 6 O) n + H] + with EC molecules decreased. 44,45 Therefore, the optimal concentration of acetone was 200 ppmv.…”

Direct detection of acetonitrile at the pptv level with photoinduced associative ionization time-of-flight mass spectrometry

“…[24][25][26] However, limited by the photon energy, which is usually below 10.6 eV, some low molecular weight VOCs, e.g., acetonitrile, with an ionization energy (12.2 eV) above the photon energy are hard to detect by PI-MS. To overcome this problem, a series of dopant-assisted photoionization techniques have been developed to broaden the range of detection targets and enhance the detection efficiency of PI-MS for specic VOC species. [27][28][29][30][31][32][33] The dopantassisted photoionization technique is actually photoinduced chemical ionization such as charge transfer, proton transfer, substitution, etc.…”