Selected ion flow tube mass spectrometry analyses of isobaric compounds methanol and hydrazine in humid air

Recent developments and applications of selected ion flow tube mass spectrometry (SIFT-MS)

Selected ion flow tube mass spectrometry (SIFT-MS) is now recognized as the most versatile analytical technique for the identification and quantification of trace gases down to the parts-per-trillion by volume, pptv, range. This statement is supported by the wide reach of its applications, from real-time analysis, obviating sample collection of very humid exhaled breath, to its adoption in industrial scenarios for air quality monitoring. This review touches on the recent extensions to the underpinning ion chemistry kinetics library and the alternative challenge of using nitrogen carrier gas instead of helium. The addition of reagent anions in the Voice200 series of SIFT-MS instruments has enhanced the analytical capability, thus allowing analyses of volatile trace compounds in humid air that cannot be analyzed using reagent cations alone, as clarified by outlining the anion chemistry involved. Case studies are reviewed of breath analysis and bacterial culture volatile organic compound (VOC), emissions, environmental applications such as air, water, and soil analysis, workplace safety such as transport container fumigants, airborne contamination in semiconductor fabrication, food flavor and spoilage, drugs contamination and VOC emissions from packaging to demonstrate the stated qualities and uniqueness of the new generation SIFT-MS instrumentation. Finally, some advancements that can be made to improve the analytical capability and reach of SIFT-MS are mentioned.

Fluorometric trace methanol detection in ethanol and isopropanol in a water medium for application in alcoholic beverages and hand sanitizers

Detection of methanol (MeOH) in an ethanol (EtOH)/isopropanol (ⁱPrOH) medium containing water is crucial to recognize MeOH poisoning in alcoholic beverages and hand sanitizers. Although chemical sensing methods are very sensitive and easy to perform, the chemical similarities between the alcohols make MeOH detection very challenging particularly in the presence of water. Herein, the fluorometric detection of a trace amount of MeOH in EtOH/ⁱPrOH in the presence of water using alcohol coordinated Al(iii)-complexes of an aldehydic phenol ligand containing a dangling pyrazole unit is described. The presence of MeOH in the EtOH/ⁱPrOH causes a change of the complex geometry from tetrahedral (Td) to octahedral (Oh) due to the replacement of the coordinated EtOH/ⁱPrOH by MeOH molecules. The Td-complex exhibited fluorescence but the Oh-species did not, because of the intramolecular photo-induced electron transfer (PET). By interacting the Oh species with water, its one MeOH coordination is replaced by a water molecule followed by the proton transfer from the water to pyrazole-N which generates strong fluorescence by inhibiting the PET. In contrast, the water interaction dissociates the Td-complex to exhibit fluorescence quenching. The water induced reversal of the fluorescence response from the decrease to increase between the absence and presence of MeOH is utilized to detect MeOH in an EtOH/ⁱPrOH medium containing water with a sensitivity of ∼0.03–0.06% (v/v). The presence of water effected the MeOH detection and allows the estimation of the MeOH contamination in alcoholic beverages and hand sanitizers containing large amounts of water.

Detection of MeOH in EtOH/ⁱPrOH and commercial samples based on water induced reversal of fluorescence response from the decrease to increase between the absence and presence of MeOH.

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

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.