Proof of Concept Coded Aperture Miniature Mass Spectrometer Using a Cycloidal Sector Mass Analyzer, a Carbon Nanotube (CNT) Field Emission Electron Ionization Source, and an Array Detector

Abstract

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.

Improving the Performance of a Cycloidal Coded-Aperture Miniature Mass Spectrometer

“…The improved C-CAMMS miniature prototype (C-CAMMS-MP) is based on the previous C-CAMMS instrument 20 and consists of a membrane inlet, a thermionic filament-based ion source, a cycloidal mass analyzer, an array detector, control electronics, and a vacuum system. The following sections describe each subsystem and the changes we made to the subcomponents in the previous C-CAMMS instrument to improve performance.…”

“…The sample inlet in the previous C-CAMMS instrument was a direct-leak inlet that used a precision needle valve to control the sample flow into the C-CAMMS ion source. 20 In the new C-CAMMS-MP instrument, samples are introduced via a polydimethylsiloxane (PDMS) membrane inlet. The membrane inlet is one of the more commonly used, passive, and selective inlet techniques for mass spectrometry.…”

“…The membrane inlet is connected to a custom gas mixing system consisting of several mass flow controllers (controlled by a LabVIEW program), pneumatic valves, and pressurized gas cylinders, as previously described. 20 The previous C-CAMMS instrument used an Agilent Technologies IDP-15 Dry Scroll vacuum pump backing an Agilent Turbo V81 M turbo pump. In their place, the new C-CAMMS-MP employs a Pfeiffer Vacuum miniature diaphragm pump (MVP-010) and a Pfeiffer Vacuum turbomolecular pump (HiPace 10) for portability.…”

“…The measurement matrix then contains off-diagonal elements representative of multiplexing and there is no longer a single set of detector elements for each m/z. After determination of the measurement matrix H from the physics and architecture of the system, a mass spectrum can be reconstructed from the coded spectrum for an unknown compound or compounds by solving the inverse problem S ̂= H −1 g, where S ̂represents an estimate of the real spectrum S. 11 Previous work demonstrated the ability of aperture coding to increase the throughput without sacrificing resolution in a 90°m agnetic sector mass analyzer, 21,23 a Mattauch−Herzog mass analyzer, 22 and a cycloidal mass analyzer, 20 all of which were coupled with a position sensitive array detector. For the 90°a nd Mattauch−Herzog instruments, a distorted image of the aperture is projected on the detector that varies for each m/z due to the physics and architecture of the mass analyzer.…”

“…These artifacts were caused by variations in the system response and aperture image as a function of position along the detector due to nonuniformities in the electric field and misalignment of the detector and the ion source with the mass analyzer focal plane. 20 This paper presents a redesign of the ion source and the electric sector from the previous C-CAMMS instrument to improve the uniformity of the aperture image and system response, thereby reducing artifacts in spectral reconstruction using a simple deconvolution algorithm. The improvement in the uniformity of aperture image and system response is achieved by improving the electric field uniformity and ensuring that the detector and the ion source are better aligned with the mass analyzer focal plane.…”