Plasma-based ambient mass spectrometry: Recent progress and applications

Ambient mass spectrometry (AMS) has grown as a group of advanced analytical techniques that allow for the direct sampling and ionization of the analytes in different statuses from their native environment without or with minimum sample pretreatments. As a significant category of AMS, plasma-based AMS has gained a lot of attention due to its features that allow rapid, real-time, high-throughput, in vivo, and in situ analysis in various fields, including bioanalysis, pharmaceuticals, forensics, food safety, and mass spectrometry imaging. Tens of new methods have been developed since the introduction of the first plasma-based AMS technique direct analysis in real-time. This review first provides a comprehensive overview of the established plasma-based AMS techniques from their ion source configurations, mechanisms, and developments. Then, the progress of the representative applications in various scientific fields in the past 4 years (January 2017 to January 2021) has been summarized. Finally, we discuss the current challenges and propose the future directions of plasma-based AMS from our perspective.

A methodological inter-comparison study on the detection of surface contaminant sodium dodecyl sulfate applying ambient- and vacuum-based techniques

Biomedical devices are complex products requiring numerous assembly steps along the industrial process chain, which can carry the potential of surface contamination. Cleanliness has to be analytically assessed with respect to ensuring safety and efficacy. Although several analytical techniques are routinely employed for such evaluation, a reliable analysis chain that guarantees metrological traceability and quantification capability is desirable. This calls for analytical tools that are cascaded in a sensible way to immediately identify and localize possible contamination, both qualitatively and quantitatively. In this systematic inter-comparative approach, we produced and characterized sodium dodecyl sulfate (SDS) films mimicking contamination on inorganic and organic substrates, with potential use as reference materials for ambient techniques, i.e., ambient mass spectrometry (AMS), infrared and Raman spectroscopy, to reliably determine amounts of contamination. Non-invasive and complementary vibrational spectroscopy techniques offer a priori chemical identification with integrated chemical imaging tools to follow the contaminant distribution, even on devices with complex geometry. AMS also provides fingerprint outputs for a fast qualitative identification of surface contaminations to be used at the end of the traceability chain due to its ablative effect on the sample. To absolutely determine the mass of SDS, the vacuum-based reference-free technique X-ray fluorescence was employed for calibration. Convex hip liners were deliberately contaminated with SDS to emulate real biomedical devices with an industrially relevant substance. Implementation of the aforementioned analytical techniques is discussed with respect to combining multimodal technical setups to decrease uncertainties that may arise if a single technique approach is adopted. Graphical abstract ᅟ.

Template for 3D Printing a Low-Temperature Plasma Probe

Low-temperature plasma (LTP) ionization represents an emerging technology in ambient mass spectrometry. LTP enables the solvent-free direct detection of a broad range of molecules and mass spectrometry imaging (MSI). The low energy consumption and modest technical requirements of these ion sources favors their employment in mobile applications and as a means to upgrade existing mass analyzers. However, the broad adoption of LTP is hindered by the lack of commercial devices, and constructing personal devices is tricky. Improper setup can result in equipment malfunction or may cause serious damage to instruments due to strong electromagnetic fields or arcing. With this in mind, we developed a reproducible LTP probe, which is designed exclusively from commercial and 3D printed components. The plasma jet generated by the device has a diameter of about 200 μm, which is satisfactory for the ambient imaging of macroscopic samples. We coupled the 3D-LTP probe to an ion trap analyzer and demonstrated the functionality of the ion source by detecting organic and chemical compounds from pure reference standards, biological substances, and pharmaceutical samples. Molecules were primarily detected in their protonated form or as water/ammonium adducts. The identification of compounds was possible by standard collision-induced dissociation (CID) fragmentation spectra. The files necessary to reproduce the 3D parts are available from the project page ( http://lababi.bioprocess.org/index.php/3d-ltp ) under a dual license model, which permits reproduction of the probe and further community-driven development for noncommercial use ("peer production"). Our reproducible probe design thus contributes to a facilitated adaption and evolution of low-temperature plasma technologies in analytical chemistry.

Mass spectrometry based chemical imaging of foods

Chemical imaging based on mass spectrometry is an emerging technology which has opened opportunities for fundamental research in food science.