Integration of paper spray ionization high‐field asymmetric
waveform ion mobility spectrometry for forensic applications
Christopher A. Tipple
Richard A. Yost
Department of Chemistry, University of
Florida, Gainesville, FL, USA
Counterterrorism and Forensic Science
Research Unit, Visiting Scientist Program,
Federal Bureau of Investigation Laboratory
Division, Quantico, VA, USA
Counterterrorism and Forensic Science
Research Unit, Federal Bureau of Investigation
Laboratory Division, Quantico, VA, USA
R. A. Yost, Department of Chemistry,
University of Florida, Gainesville, FL, USA.
Oak Ridge Institute for Science and Education
Paper spray ionization (PSI) is an attractive ambient ionization source for mass
spectrometry (MS) since it allows the combination of surface sampling and ionization. The
minimal sample preparation inherent in this approach greatly reduces the time needed for
analysis. However, the ions generated from interfering compounds in the sample and the paper
substrate may interfere with the analyte ions. Therefore, the integration of PSI with high‐field
asymmetric ion mobility spectrometry (FAIMS) is of significant interest since it should reduce
the background ions entering the mass analyzer without complicating the analysis or increasing
analysis time. Here we demonstrate the integration of PSI with FAIMS/MS and its potential for
analysis of samples of forensic interest.
In this work, the parameters that can influence the integration, including sampling
and ionization by paper spray, the FAIMS separation of analytes from each other and background
interferences, and the length of time that a usable signal can be observed for explosives on paper,
were evaluated with the integrated system.
In the negative ion analysis of 2,4,6‐trinitrotoluene (TNT), pentaerythritol tetranitrate
(PETN), octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocine (HMX), and 1,3,5‐trinitroperhydro‐1,3,5‐
triazine (RDX), amounts as low as 1 ng on paper were readily observed. The successful positive ion
separation of a set of illicit drugs including heroin, methamphetamine, and cocaine was also
achieved. In addition, the positive ion analysis of the chemical warfare agent simulants dimethyl
methylphosphonate (DMMP) and diisopropyl methylphosphonate (DIMP) was evaluated.
The integration of PSI‐FAIMS/MS was demonstrated for the analyses of
explosives in negative ion mode and for illicit drugs and CW simulants in positive mode. Paper
background ions that could interfere with these analyses were separated by FAIMS. The
compensation voltage of an ion obtained by FAIMS provided an additional identification parameter
to be combined with the mass spectrum for each analyte.
Wipes or swabs are commonly employed media for surface sampling
methods used in forensic sample collection protocols. The preparation
of wipes or swabs prior to sampling and the extraction steps needed
prior to instrumental analysis can be time‐consuming. In addition, these
samples are often quite complex, requiring extensive chromatographic
methods for their analysis, which takes more time to complete. A
recent focus in mass spectrometric research involves the development
of ambient ionization sources in which samples are ionized under
ambient conditions with minimal sample preparation that can reduce
One such technique, paper spray ionization (PSI),
developed by Wang et al,
is of particular interest. The setup of PSI
is simple. In addition, the ionization mechanism is theorized to be the
same as electrospray ionization (ESI). Therefore, analyses that are
typically performed using ESI could potentially be performed using
PSI. Applications of PSI to the analysis of pharmaceuticals in dry blood
spots, urine samples, and other samples have been demonstrated.
Using such an approach, forensically relevant samples can be analyzed
in a quicker fashion. This not only helps to reduce any potential backlogs,
but also reduces solvent waste and the overall cost of the analysis.
Despite the advantages of PSI, there are practical challenges.
One such challenge that could limit its application is the presenceof back-
ground interferences resulting from the paper substrate. In a previous
This article has been contributed to by US Government employees and their work is in the public domain in the USA.
Received: 25 August 2017 Revised: 30 November 2017 Accepted: 20 January 2018
552 Copyright © 2018 John Wiley & Sons, Ltd. Rapid Commun Mass Spectrom. 2018;32:552–560.wileyonlinelibrary.com/journal/rcm