In 1938, Walker Bleakney and John A. Hipple first described the cycloidal mass analyzer as the only mass analyzer configuration capable of "perfect" ion focusing. Why has their geometry been largely neglected for many years and how might it earn a respectable place in the world of modern chemical analysis? This Perspective explores the properties of the cycloidal mass analyzer and identifies the lack of suitable ion array detectors as a significant reason why cycloidal mass analyzers are not widely used. The recent development of capacitive transimpedance amplifier array detectors can enable several techniques using cycloidal mass analyzers including spatially coded apertures and single particle mass analysis with a "virtual-slit", helping the cycloidal mass analyzer earn a respectable place in chemical analysis.

This work demonstrates a novel approach to mass spectrometry using the "virtual-slit" created by the small, localized volume from which ions are generated by localized ionization techniques such as laser ionization of particles and surfaces, and spark ionization. That is, the volume in which the ions are generated creates a localized source of ions in much the same way as a slit that allows only ions from a specific cross sectional area to pass. As demonstrated in this work, the unique perfect focusing properties of a cycloidal mass analyzer can enable the localized ionization volume to function as a virtual-slit. In this manuscript, we provide a proof-of-concept (POC) demonstration of a virtual-slit cycloidal mass spec-trometer (VS-CMS) consisting of a cycloidal mass analyzer, a laser ionization source, and an ion array detector. The laser is used to ionize either bulk or thin film samples of Cu, Ti, Ni, and Cr. Results indicate that the width of the peaks at the detector is the same as the laser spot size, validating the concept of virtual-slit focusing. Furthermore, the Ti and Cu ablated with each laser pulse is estimated at 60 and 140 fg, respectively, indicating that a very low detection limit is possible given the ability of the cycloidal mass analyzer to collect ions generated by laser ionization that have wide energy and angular disper-sions. The VS-CMS concept has the potential to enable development of fieldable instruments for chemical, elemental, and isotopic analysis of organic and inorganic samples, that are relatively small compared to currently used laser ionization time-of-flight and laser ablation inductively coupled plasma mass spectrometers. (c) 2021 Elsevier B.V. All rights reserved.

Cycloidal sector mass analyzers have, in principle, perfect focusing due to perpendicularly oriented uniform electric and magnetic fields, making them ideal candidates for incorporation of spatially coded apertures. We have previously demonstrated a proof-of-concept cycloidal-coded aperture miniature mass spectrometer (C-CAMMS) instrument and achieved a greater than 10-fold increase in throughput without sacrificing resolution, compared with a single slit instrument. However, artifacts were observed in the reconstructed mass spectrum due to nonuniformity in the electric field and misalignment of the detector and the ion source with the mass analyzer focal plane. In this work, we modified the mass analyzer design of the previous C-CAMMS instrument to improve electric field uniformity, improve the alignment of the ion source and the mass analyzer with the detector, and increase the depth-of-focus to further facilitate alignment. A comparison of reconstructed spectra of a mixture of dry air and toluene at different electric fields was performed using the improved C-CAMMS prototype. A reduction in reconstruction artifacts compared to our proof-of-concept C-CAMMS instrument highlights the improved performance enabled by the design changes.

This work compares the coded aperture imaging performance of thermionic filament and carbon nanotube (CNT) field emitter-based electron sources in cycloidal-coded aperture mass spectrometers. The use of spatially coded apertures in mass spectrometry enables miniaturization by improving throughput without sacrificing resolution. CNT-based electron ionization sources for mass spectrometers provide several potential benefits over conventional thermionic emitters, including low voltage and low power consumption, room temperature operation, long lifetime, and ability to emit electrons in a pulsed mode. However, spatiotemporal variation in electron emission from CNTs is a major disadvantage. In this study, electron emission stability and spatiotemporal stability of the coded aperture image were compared for coded aperture cycloidal mass analyzers with either a CNT-based ion source or a thermionic filament-based ion source. We found that the thermionic filament-based ion source produced a significantly more stable coded aperture image than the CNT based ion source. The aperture image fluctuations in the CNT-based source are likely a result of adsorption and desorption of molecules on the CNT surface that cause local work function changes and induce spatiotemporal variation in electron emission and subsequent ion generation.

Despite many potential applications, miniature mass spectrometers have had limited adoption in the field due to the tradeoff between throughput and resolution that limits their performance relative to laboratory instruments. Recently, a solution to this tradeoff has been demonstrated by using spatially coded apertures in magnetic sector mass spectrometers, enabling throughput and signal-to-background improvements of greater than an order of magnitude with no loss of resolution. This paper describes a proof of concept demonstration of a cycloidal coded aperture miniature mass spectrometer (C-CAMMS) demonstrating use of spatially coded apertures in a cycloidal sector mass analyzer for the first time. C-CAMMS also incorporates a miniature carbon nanotube (CNT) field emission electron ionization source and a capacitive transimpedance amplifier (CTIA) ion array detector. Results confirm the cycloidal mass analyzer's compatibility with aperture coding. A >10× increase in throughput was achieved without loss of resolution compared with a single slit instrument. Several areas where additional improvement can be realized are identified. Graphical Abstract ᅟ.

The use of microelectromechanical systems (MEMS) components in miniature mass spectrometers is particularly attractive due to their small size and scalable manufacturing capability. Our group has pioneered the development of miniature electron ionization sources combining MEMS fabricated structures with integrated carbon nanotube (CNT) cold-cathode field emitters. However, until now they have been of limited use due to the limited ability to direct the ions into a mass analyzer. In this work, we design a miniature ion source using a microfabricated MEMS device and a low temperature co-fired ceramic (LTCC) carrier that includes electrical connections, ion optics for directing ions out of the device, and a sample inlet. We present the design and fabrication of the ion source; simulate the energy and angular dispersion; and experimentally determine the energy and angular dispersion. (C) 2016 Elsevier B.V. All rights reserved.

A fourth-generation focal plane camera containing 1696 Faraday-strip detectors was fitted to a Mattauch-Herzog mass spectrograph and characterized for its performance with inductively coupled plasma ionization. The camera provides limits of detection in the single to tens of ng L-1 range for most elements and has a linear dynamic range of at least nine orders of magnitude. Isotope-ratio precision better than 0.02% has also been achieved with this device, and this fourth-generation system features the broadest simultaneous mass range obtainable to date with this family of focal plane camera detectors.

A micro-Faraday array detector (row of miniature 32 thin film strip electrodes wire bonded to an on-chip integrated capacitance transimpedance amplifier) was tested for use in a multiple collector secondary ion mass spectrometry. The detector was mounted on a standard IMS3f SIMS instrument in place of a microchannel plate. The measurements were performed by using a silicon sample bombarded by either or Cs+ primary ions with or without D2O flooding and detecting secondary ions of Si±, SiH±, O-, SiD−, OD−. A parallel detection of near masses of 29Si and 28SiH or 18O and 16OD was demonstrated at a sensitivity level ∼230 counts/s.

An ambient desorption/ionization (ADI) source, known as the flowing atmospheric pressure afterglow (FAPA), has been coupled to a Mattauch-Herzog mass spectrograph (MHMS) equipped with a focal plane camera (FPC) array detector. The FAPA ionization source enables direct mass spectral analysis of solids, liquids, and gases through either positive or negative ionization modes. In either case, spectra are generally simple with dominant peaks being the molecular ions or protonated molecular ions. Use of the FAPA source with the MHMS allows the FPC detector to be characterized for the determination of molecular species, whereas previously only atomic mass spectrometry (MS) has been demonstrated. Furthermore, the FPC is shown to be sensitive to negative ions without the need to change any detector parameters. The analysis of solid, liquid, and gaseous samples through positive and negative ionization is demonstrated with detection limits (1–25 fmol/s, ∼0. 3–10 pg of analyte per mL of helium) surpassing those obtained with the FAPA source coupled to a time-of-flight mass analyzer.

Isotope-ratio measurements are necessary in a wide range of applications. The precision of these measurements is of utmost importance because it governs the ability to distinguish differences between samples. Often, simultaneous isotope detection is necessary to reach the precision values needed for an analysis to be conclusive. Furthermore, the more isotope ratios that can be precisely determined at once, the better the chances of distinguishing between samples. Therefore, detector arrays, able to simultaneously monitor a broad range of isotopes, are attractive. Such an array detector, termed the focal plane camera (FPC), has been shown to be capable of achieving impressive precision values (0.02% RSD) within relatively short integration times (200 s). However, because the channels of the FPC array detector are inherently discrete, optimization of peak integration methods is important. This paper compares isotope-ratio precision values based on different peak integration methods of raw and zero-filled interpolated data. Also, problems associated with peak drift are explored and the use of flat-topped peak shapes for improved isotope-ratio precision levels are investigated.

A third-generation Faraday-strip array detector has been coupled to a Mattauch-Herzog mass spectrometer and dc glow-discharge ionization source. This combination offers simultaneous determination of multiple elements directly from solid samples and provides superior resolving power and improved limits of detection over previous generations of array detectors. With the third-generation detector array, resolving power is limited only by the mass spectrometer and not by the array. Because of this enhanced resolution, limits of detection, especially for higher mass-to-charge ratios, were improved. Isotope-ratio precision was found to be 0.07% RSD on average and quantitative response was linear over 5 orders of magnitude.

A 512-channel Faraday-strip array detector has been developed and fitted to a Mattauch-Herzog geometry mass spectrograph for the simultaneous acquisition of multiple mass-to-charge values. Several advantages are realized by using simultaneous detection methods, including higher duty cycles, removal of correlated noise, and multianalyte transient analyses independent of spectral skew. The new 512-channel version offers narrower, more closely spaced pixels, providing improved spectral peak sampling and resolution. In addition, the electronics in the amplification stage of the new detector array incorporate a sample-and-hold feature that enables truly simultaneous interrogation of all 512 channels. While sensitivity and linear dynamic range remain impressive for this Faraday-based detector system, limits of detection and isotope ratio data have suffered slightly from leaky p-n junctions produced during the manufacture of the semiconductor-based amplification and readout stages. This paper describes the new 512-channel detector array, the current dominant noise sources, and the figures of merit for the device as pertaining to inductively coupled plasma ionization.