Miniature flowing atmospheric-pressure afterglow ion source for facile interfacing of CE with MS

Glow flow ionization mass spectrometry of small molecules. A comparison of a glow flow ionization source ('GlowFlow') with electrospray ionization and atmospheric pressure chemical ionization

RATIONALE

Ionization by atmospheric pressure gas discharge has been employed for a long time in mass spectrometry. Inductively coupled plasma mass spectrometry is an exemplar, and widely used for elemental analysis. The technique has less uptake in organic mass spectrometry. We describe a simple source design that can be readily implemented in most atmospheric pressure ionization (API) systems and compare its performance with that of electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI).

METHODS

An in-house designed helium gas discharge source (referred to as 'GlowFlow') was used on a Xevo G2-S time-of-flight mass spectrometer. The GlowFlow source was transferred to a compatible Xevo TQ-S triple-quadrupole mass spectrometer using an ultrahigh-performance liquid chromatograph inlet. Its performance was compared to that of Waters ESI and APCI sources.

RESULTS

Preliminary results of GlowFlow on the Swansea instrument are presented to establish context and include analysis of low-molecular-mass polymers, benzoic acid and cinnamic acid. Comparison of performance on the Xevo TQ-S triple-quadrupole mass spectrometer involved three test mixtures. The method limits of detection (six-mix) for positive-ion GlowFlow source were between 0.03 and 10.00 pg with good linear response over two to four orders of magnitude and values of R²  > 0.98. The GlowFlow ionization source provided a signal intensity that was an order of magnitude greater than that of ESI for an atmospheric pressure gas chromatography standard mix and ionized several compounds that ESI could not.

CONCLUSIONS

The current GlowFlow design is relatively simple to retrofit to most API systems due to its small size. The sensitivity of the GlowFlow design is typically an order of magnitude less than that of ESI in positive-ion mode, but similar in sensitivity in negative-ion mode and comparable to that of APCI.

LASER DESORPTION/ABLATION POSTIONIZATION MASS SPECTROMETRY: RECENT PROGRESS IN BIOANALYTICAL APPLICATIONS

Lasers have long been used in the field of mass spectrometric analysis for characterization of condensed matter. However, emission of neutrals upon laser irradiation surpasses the number of ions. Typically, only one in about one million analytes ejected by laser desorption/ablation is ionized, which has fueled the quest for postionization methods enabling ionization of desorbed neutrals to enhance mass spectrometric detection schemes. The development of postionization techniques can be an endeavor that integrates multiple disciplines involving photon energy transfer, electrochemistry, gas discharge, etc. The combination of lasers of different parameters and diverse ion sources has made laser desorption/ablation postionization (LD/API) a growing and lively research community, including two-step laser mass spectrometry, laser ablation atmospheric pressure photoionization mass spectrometry, and those coupled to ambient mass spectrometry. These hyphenated techniques have shown potentials in bioanalytical applications, with major inroads to be made in simultaneous location and quantification of pharmaceuticals, toxins, and metabolites in complex biomatrixes. This review is intended to provide a timely comprehensive view of the broadening bioanalytical applications of disparate LD/API techniques. We also have attempted to discuss these applications according to the classifications based on the postionization methods and to encapsulate the latest achievements in the field of LD/API by highlighting some of the very best reports in the 21st century. © 2020 John Wiley & Sons Ltd.

MINIATURIZATION IN MASS SPECTROMETRY

Expectations for continuous miniaturization in mass spectrometry are not declining for years. Portable instruments are highly welcome by the industry, science, space agencies, forensic laboratories, and many other units. All are striving for the small, cheap, and as good as possible instruments. This review describes the recent developments of miniature mass spectrometers and also provides selected applications where these devices are used. Upcoming perspectives of further development are also discussed. @ 2019 John Wiley & Sons Ltd. Mass Spec Rev.

Online coupling techniques in ambient mass spectrometry

Since ambient mass spectrometry (AMS) has been proven to have low matrix effects and high salt tolerance, great efforts have been made for online coupling of several analytical techniques with AMS. These analytical techniques include gas chromatography (GC), liquid chromatography (LC), capillary electrophoresis (CE), surface plasmon resonance (SPR), and electrochemistry flow cells. Various ambient ionization sources, represented by desorption electrospray ionization (DESI) and direct analysis in real time (DART), have been utilized as interfaces for the online coupling techniques. Herein, we summarized the advances in these online coupling methods. Close attention has been paid to different interface setups for coupling, as well as limits of detection, tolerance to different matrices, and applications of these new coupling techniques.

Plasma-based ambient ionization mass spectrometry in bioanalytical sciences

Plasma-based ambient ionization mass spectrometry techniques are gaining growing interest due to their specific features, such as the need for little or no sample preparation, its high analysis speed, and the ambient experimental conditions. Samples can be analyzed in gas, liquid, or solid forms. These techniques allow for a wide range of applications, like warfare agent detection, chemical reaction control, mass spectrometry imaging, polymer identification, and food safety monitoring, as well as applications in biomedical science, e.g., drug and pharmaceutical analysis, medical diagnostics, biochemical analysis, etc. Until now, the main drawback of plasma-based techniques is their quantitative aspect, but a lot of efforts have been done to improve this obstacle.

Online monitoring of molecular processes in a plasma air purifying system

Plasma air purifying systems present an interesting alternative to filters for purifying air. In this study, molecular processes in a commercially available ac driven plasma air purifier were studied in detail. This air purifier is supposed to reduce all air contaminants to small nontoxic molecules (e.g., H(2)O and CO(2)). However, degradation mechanisms are not yet fully understood. In this study, we investigated the exhaust of the plasma air purifier to determine which degradation products are formed. An interface was designed and constructed to allow the direct coupling of the plasma air purifier's exhaust to a mass spectrometer. The compounds studied, primary and secondary amines, were introduced at a concentration of 1 ppmV. Contrary to our expectations, polymerization instead of degradation was observed. The higher the ac voltage applied (max. 9.0 kV) to the plasma air purifier, the higher the mass of the oligomer distribution. Side chain oxidation products as well as oligomers could be observed for all compounds tested. Starting with amines of low mass (m/z < 200), compounds of molecular masses above 1000 Da were observed in the plasma air purifier. Detailed analysis of the observed mass spectra as well as experiments with deuterated dibutylamine helped to unravel the mechanism taking place in the plasma air purifier. Nitrate anions generated in the plasma air purifier (presumably from N(2)) are proposed to form ionic clusters with protonated amines.