A call for more science in forensic science Bell, Suzanne; Sah, Sunita; Albright, Thomas D. ...
Proceedings of the National Academy of Sciences - PNAS,
05/2018, Volume:
115, Issue:
18
Journal Article
Peer reviewed
Open access
Forensic science is critical to the administration of justice. The discipline of forensic science is remarkably complex and includes methodologies ranging from DNA analysis to chemical composition to ...pattern recognition. Many forensic practices developed under the auspices of law enforcement and were vetted primarily by the legal system rather than being subjected to scientific scrutiny and empirical testing. Beginning in the 1990s, exonerations based on DNA-related methods revealed problems with some forensic disciplines, leading to calls for major reforms. This process generated a National Academy of Science report in 2009 that was highly critical of many forensic practices and eventually led to the establishment of the National Commission for Forensic Science (NCFS) in 2013. The NCFS was a deliberative body that catalyzed communication between nonforensic scientists, forensic scientists, and other stakeholders in the legal community. In 2017, despite continuing problems with forensic science, the Department of Justice terminated the NCFS. Just when forensic science needs the most support, it is getting the least. We urge the larger scientific community to come to the aid of our forensic colleagues by advocating for urgently needed research, testing, and financial support.
With the advent of technologies such as ion array detectors and high energy permanent magnet materials, there is renewed interest in the unique focusing properties of the cycloidal mass analyzer and ...its ability to enable small, high‐resolution, and high‐sensitivity instruments. However, most literature dealing with the design of cycloidal mass analyzers assumes a single channel detector because at the time of those publications, compatible multichannel detectors were not available. This manuscript introduces and discusses considerations and a procedure for designing cycloidal mass analyzers coupled with focal plane ion array detectors. To arrive at a set of relevant design considerations, we first review the unique focusing properties of the cycloidal mass analyzer and then present calculations detailing how the dimensions and position of the focal plane array detector relative to the ion source determine the possible mass ranges and resolutions of a cycloidal mass analyzer. We present derivations and calculations used to determine the volume of homogeneous electric and magnetic fields needed to contain the ion trajectories and explore the relationship between electric and magnetic field homogeneity on resolving power using finite element analysis (FEA) simulations. A set of equations relating the electric field homogeneity to the geometry of the electric sector electrodes was developed by fitting homogeneity values from 78 different FEA models. Finally, a sequence of steps is suggested for designing a cycloidal mass analyzer employing an array detector.
Spatial aperture coding is a technique used to improve throughput without sacrificing resolution both in optical spectroscopy and sector mass spectrometry (MS). Previous work demonstrated that ...aperture coding combined with a position-sensitive array detector in a miniature cycloidal mass spectrometer was successful in providing high-throughput, high-resolution measurements. However, due to poor alignment and field nonuniformities, reconstruction artifacts were present. Recently, significant progress was made in eliminating most of the reconstruction artifacts with improved field uniformity and alignment. However, artifacts as large as 1/3 of the main peak were still observed at low mass (<17 u). Such artifacts will reduce accuracy in identification and quantification of analytes, reducing the impact of the throughput advantage gained by using a coded aperture. The artifacts were hypothesized to be a result of a mass dependent in curvature of ions in the ion source. Ions with higher mass (m/z > 17 u) and a larger curvature did not pass through all slits in the coded aperture. Therefore, when reconstructing with a system response derived from the aperture image from a higher mass m/z = 32 u ion, reconstruction artifacts appeared for m/z < 17 u. In this work, two methods were implemented to significantly reduce the presence of artifacts in reconstructed data. First, we modified the reconstruction algorithm to incorporate a mass-dependent system response function across the mass range (10–110 u). This method reduced the size of the artifacts by 82%. Second, to validate the hypothesis that the mass-dependent system response function was a result of differences in curvature of ions in the ion source, we modified the design of the ion source by shifting the coded aperture slits relative to the center of the ionization volume. This method resulted in ions of all masses passing through all slits in the coded aperture, a constant system response function across the entire mass range. Artifacts were reduced by 94%.
Higher resolution in fieldable mass spectrometers (MS) is desirable in space flight applications to enable resolving isobaric interferences at m/z < 60 u. Resolution in portable cycloidal MS coupled ...with array detectors could be improved by reducing the slit width and/or by reducing the width of the detector pixels. However, these solutions are expensive and can result in reduced sensitivity. In this paper, we demonstrate high-resolution spectral reconstruction in a cycloidal coded aperture miniature mass spectrometer (C-CAMMS) without changing the slit or detector pixel sizes using a class of signal processing techniques called super-resolution (SR).
We developed an SR reconstruction algorithm using a sampling SR approach whereby a set of spatially shifted low-resolution measurements are reconstructed into a higher-resolution spectrum. This algorithm was applied to experimental data collected using the C-CAMMS prototype. It was then applied to synthetic data with additive noise, system response variation, and spatial shift nonuniformity to investigate the source of reconstruction artifacts in the experimental data.
Experimental results using two ½ pixel shifted spectra resulted in a resolution of ¾ pixel full width at half maximum (FWHM) at m/z = 28 u. This resolution is equivalent to 0.013 u, six times better than the resolution previously published at m/z = 28 for N
using C-CAMMS. However, the reconstructed spectra exhibited some artifacts. The results of the synthetic data study indicate that the artifacts are most likely caused by the system response variation.
This paper demonstrates super-resolution spectral reconstruction in C-CAMMS without changing the slit or detector pixel sizes using a sampling SR approach. With improvements, this technique could be used to resolve isobaric interferences in a portable cycloidal MS for space flight applications.
The improvised explosive triacetone triperoxide (TATP) was synthesized and characterized by
1H-nuclear magnetic resonance (NMR),
13C-NMR, Raman and infrared (IR) spectroscopy. Triacetone triperoxide ...was subsequently analyzed by ion mobility spectrometry (IMS) in positive ion mode, and detected as a cluster of three peaks with a drift time of the most intense peak at 13.06
ms. Triacetone triperoxide was then analyzed after dissolution in toluene, where a dramatic increase in peak intensity was observed, at a flight time of 12.56
ms (
K
0=2.71
cm
2
V
−1
s
−1). Triacetone triperoxide was subsequently analyzed by coupling the ion mobility spectrometer to a triple quadrupole mass spectrometer, where a single peak at
m/
z of 223 atomic mass units identified the species present in the ion mobility spectra as being triacetone triperoxide.
The Long Neglected Cycloidal Mass Analyzer Piacentino, Elettra L; Serpa, Rafael Bento; Horvath, Kathleen L ...
Analytical chemistry (Washington),
08/2021, Volume:
93, Issue:
33
Journal Article
Peer reviewed
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.
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
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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.
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.
MS Detectors Koppenaal, David W; Barinaga, Charles J; Denton, M. Bonner ...
Analytical chemistry (Washington),
11/2005, Volume:
77, Issue:
21
Journal Article
Peer reviewed
Open access
Just as laser eye surgery has restored fading human vision, new technologies are needed to improve ion "chemical vision" detection. Koppenaal et al discuss current mass spectrometry detector ...technology and provide a glimpse of the future.
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