Yuichiro Hashimoto

Development of a portable mass spectrometer characterized by discontinuous sample gas introduction, a low-pressure dielectric barrier discharge ionization source, and a vacuumed headspace technique.

The present study has attempted to downscale a mass spectrometer in order to make it portable and enable onsite analysis with it. The development of a small mass spectrometer required the use of a compact pump whose displacement was small, decreasing the sensitivity of that spectrometer. To get high sensitivity with a small mass spectrometer, we have integrated novel techniques: a highly sensitive ionization source and efficient extraction of sample vapor. The low-pressure dielectric barrier discharge ionization (LP-DBDI) source made it possible to increase the conductance between the source and the mass analyzer, compared with ambient ionization sources, enhancing the efficiency of the ion transfer from the ionization source to the mass analyzer. We have also developed a vacuumed headspace method efficiently transporting the sample vapor to the ionization source. The sensitivity was further enhanced by also using a discontinuous sample gas introduction technique. A prototype portable mass spectrometer using those novel techniques was found to be sensitive enough to detect 0.1 ppm methamphetamine, 1 ppm amphetamine, 1 ppm 3,4-methylenedioxymethamphetamine, and 10 ppm cocaine in liquid.

High-throughput walkthrough detection portal for counter terrorism: detection of triacetone triperoxide (TATP) vapor by atmospheric-pressure chemical ionization ion trap mass spectrometry.

With the aim of improving security, a high-throughput portal system for detecting triacetone triperoxide (TATP) vapor emitted from passengers and luggage was developed. The portal system consists of a push-pull air sampler, an atmospheric-pressure chemical ionization (APCI) ion source, and an explosives detector based on mass spectrometry. To improve the sensitivity of the explosives detector, a novel linear ion trap mass spectrometer with wire electrodes (wire-LIT) is installed in the portal system. TATP signals were clearly obtained 2 s after the subject under detection passed through the portal system. Preliminary results on sensitivity and throughput show that the portal system is a useful tool for preventing the use of TATP-based improvised explosive devices by screening persons in places where many people are coming and going.

High-Throughput Walkthrough Detection Portal as a Measure for Counter Terrorism: Design of a Vapor Sampler for Detecting Triacetone Triperoxide Vapor by Atmospheric-Pressure Chemical-Ionization Ion-Trap Mass Spectrometry

Aiming to prevent terrorist attacks in places where many people are coming and going, we have been developing a “high-throughput detection portal system.” The portal system consists of a vapor sampler, an atmospheric-pressure chemical-ionization ion source, and an explosives detector based on ion-trap mass spectrometry. The vapor sampler was designed to be installed in an automated ticket gate of a train station. By optimizing the shape of the nozzle that controls the air flow of the vapor sampler, triacetone triperoxide (TATP) vapor could be detected at a high throughput, i.e., 1200 persons/hour. The false-positive rate of the detection portal system for TATP was evaluated by a field test performed at a train station. A multi-marker logic to determine whether TATP existed or not was adopted, and no false-positive alarms were obtained for over 3000 passengers during the field test. However, acetone, which is an inflammable liquid, was accidentally detected from the passengers during the field test. It is concluded from this detection result that this detection portal system is useful for detecting dangerous chemicals that have high vapor pressure (such as TATP and inflammable liquids) in places where many people are coming and going.

Mass-selective axial ejection from a linear ion trap with a direct current extraction field

We have developed a new mass-selective axial ejection method from a linear ion trap (LIT). In this method, a set consisting of a trap wire lens and an extraction wire lens positioned orthogonally to each other was placed between quadrupole rods. The trap wire lens confines the ions inside the trap, and the extraction wire axially extracts ions from the trap. Ions introduced into the LIT are trapped between the inlet lens and the trap wire lens. In addition to the wire lenses, a set of excitation lenses, which are aligned orthogonally to the trap wire lens, are inserted between rods. The ions are resonantly excited in the direction perpendicular to the trap wire lens by applying a supplemental alternating current (AC) to the excitation lenses. Excited ions with a large motion pass over the trap wire lens, while unexcited ions remain trapped inside. Ions that have passed over the trap wire lens are then extracted by the extraction wire lens. The characteristics of the mass-selective ejection with a direct current (DC) extraction field were investigated by both simulation and experiment. A mass resolving power of m/Deltam = 1300 was achieved at a scan rate of 500 Th/s. The dependence of the ejection efficiency on trap wire lens bias was measured, and an ejection efficiency of 20% at a scan rate of 500 Th/s was achieved by optimizing the DC bias on the trap wire lens.

Sensitive low‐pressure dielectric barrier discharge ion source

RATIONALE We developed a novel highly sensitive soft ionization method: a low-pressure dielectric barrier discharge ionization (LP-DBDI) source. In this configuration, samples pass through the inside of a dielectric barrier discharge (DBD). Since samples pass through a DBD and its plasma jet, high ionization efficiency is expected. Furthermore, high transmission efficiency from the ion source to the mass spectrometer is also expected since the ion source is placed in a vacuum. METHODS Mass spectrometric detection was carried out in positive ion mode using an ion trap mass spectrometer. The LP-DBDI source or a conventional atmospheric pressure chemical ionization (APCI) source was attached to the mass spectrometer. Samples were vaporized and sent to ion sources with air flowing at a constant flow rate of 1.5 L/min. The LP-DBDI source was compared with a conventional APCI source. RESULTS Mass spectra of methyl salicylate, 2-undecanone and methamphetamine were acquired using the LP-DBDI source. Protonated molecules were mainly observed in the mass spectra. The sensitivities for methyl salicylate and 2-undecanone obtained using the LP-DBDI source were 44 times and 39 times higher, respectively, than those obtained using an APCI source. CONCLUSIONS LP-DBDI is a soft ionization method characterized by only minor fragmentation, similar to APCI. The sensitivity of the LP-DBDI source was found to be about 40 times higher than that of the conventional APCI source.

Mass spectra separation for explosives detection by using probabilistic latent component analysis

We propose a new method to separate mass spectra into components of each chemical compound for explosives detection. In mass spectra, all components have no negative values. However, conventional factor analyses for basis decomposition use no constraints of non-negativity, and we can not apply these methods to mass spectra. The proposed method is based on probabilistic latent component analysis (PLCA). The constraints of non-negativity always hold in PLCA, so that the method is effective for mass spectra. In addition, PLCA is defined in a statistical framework, thus PLCA makes it possible to utilize additional a priori information. Therefore, we introduce sparseness assumptions in the domain of mass spectrometry to PLCA in order to estimate the components more accurately. Experimental results indicate that the proposed method outperforms existing methods.

Probe Heating Method for the Analysis of Solid Samples Using a Portable Mass Spectrometer

We previously reported on the development of a portable mass spectrometer for the onsite screening of illicit drugs, but our previous sampling system could only be used for liquid samples. In this study, we report on an attempt to develop a probe heating method that also permits solid samples to be analyzed using a portable mass spectrometer. An aluminum rod is used as the sampling probe. The powdered sample is affixed to the sampling probe or a droplet of sample solution is placed on the tip of the probe and dried. The probe is then placed on a heater to vaporize the sample. The vapor is then introduced into the portable mass spectrometer and analyzed. With the heater temperature set to 130°C, the developed system detected 1 ng of methamphetamine, 1 ng of amphetamine, 3 ng of 3,4-methylenedioxymethamphetamine, 1 ng of 3,4-methylenedioxyamphetamine, and 0.3 ng of cocaine. Even from mixtures consisting of clove powder and methamphetamine powder, methamphetamine ions were detected by tandem mass spectrometry. The developed probe heating method provides a simple method for the analysis of solid samples. A portable mass spectrometer incorporating this method would thus be useful for the onsite screening of illicit drugs.

Real‐time explosive particle detection using a cyclone particle concentrator

RATIONALE There is a need for more rapid methods for the detection of explosive particles. We have developed a novel real-time analysis technique for explosive particles that uses a cyclone particle concentrator. This technique can analyze sample surfaces for the presence of particles from explosives such as TNT and RDX within 3 s, which is much faster than is possible by conventional methods. METHODS Particles are detached from the sample surface with air jet pulses, and then introduced into a cyclone particle concentrator with a high pumping speed of about 80 L/min. A vaporizer placed at the bottom of the cyclone particle concentrator immediately converts the particles into a vapor. The vapor is then ionized in the atmospheric pressure chemical ionization (APCI) source of a linear ion trap mass spectrometer. RESULTS An online connection between the vaporizer and a mass spectrometer enables high-speed detection within a few seconds, compared with the conventional off-line heating method that takes more than 10 s to raise the temperature of a sample filter unit. Since the configuration enriched the number density of explosive particles by about 80 times compared with that without the concentrator, a sub-ng amount of TNT particles on a surface was detectable. CONCLUSIONS The detection limit of our technique is comparable with that of an explosives trace detector using ion mobility spectrometry. The technique will be beneficial for trace detection in security applications, because it detects explosive particles on the surface more speedily than conventional methods.

Elucidating the sequence of intact bioactive peptides by using electron capture dissociation and hot electron capture dissociation in a linear radio-frequency quadrupole ion trap.

RATIONALE Electron capture dissociation (ECD) is useful tool for sequencing of peptides and proteins with post-translational modifications. To increase the sequence coverage for peptides and proteins, it is important to develop ECD device with high fragmentation efficiency. METHODS Sequence analysis of intact undigested bioactive peptides (3000-5000 Da) was performed by use of electron capture dissociation (rf-ECD) and collision-induced dissociation (CID) in a linear radio-frequency quadrupole ion trap that was coupled to a time-of-flight mass spectrometer. We applied rf-ECD, hot rf-ECD (rf-ECD with high electron energy), and CID for intact bioactive peptide ions of various charge states and evaluated the sequence coverage of their fragment spectra. RESULTS Hot rf-ECD produced a higher number of c- and z-type fragment ions of modified peptide ions as electron energy increased in lower charged peptide ions, and sequence coverage greater than 80% was obtained compared with the CID case (40-80%). CONCLUSIONS The result indicates that intact bioactive modified peptides (Ghrelin, ANP) were correctly identified by use of hot rf-ECD.

Development of a Miniature Mass Spectrometer and an Automated Detector for Sampling Explosive Materials

The development of a robust ionization source using the counter-flow APCI, miniature mass spectrometer, and an automated sampling system for detecting explosives are described. These development efforts using mass spectrometry were made in order to improve the efficiencies of on-site detection in areas such as security, environmental, and industrial applications. A development team, including the author, has struggled for nearly 20 years to enhance the robustness and reduce the size of mass spectrometers to meet the requirements needed for on-site applications. This article focuses on the recent results related to the detection of explosive materials where automated particle sampling using a cyclone concentrator permitted the inspection time to be successfully reduced to 3 s.