Minoru Sakairi

Micellar electrokinetic chromatography—mass spectrometry using a high-molecular-mass surfactant on-line coupling with an electrospray ionization interface

On-line coupling between micellar electrokinetic chromatography (MEKC) and mass spectrometry (MS) was studied with a high-molecular-mass surfactant and an electrospray ionization interface (ESI). A high-molecular-mass surfactant, butyl acrylate-butyl methacrylate-methacrylic acid copolymer sodium salt (BBMA), was employed as a pseudo-stationary phase for an on-line MEKC-MS system. BBMA and a minor component separated by size-exclusion chromatography were determined by ESI-MS. No major ion from the BBMA polymer was detected. The BBMA micelle functioned successfully as the pseudo-stationary phase in a 10 mM ammonium formate buffer containing 10% methanol. Five standard compounds, phenyltrimethylammonium chloride, 1-naphthylamine, quinine sulfate, tetraphenylphosphonium chloride and octaoxyethylenedodecanol, were separated by MEKC and detected by MS. The effects of the concentrations of BBMA on the separation and sensitivity in MEKC-MS were studied. MEKC-MS with BBMA was applied to the separation and detection of a standard mixture of sulfamides.

A sonic spray interface for the mass analysis of highly charged ions from protein solutions at high flow rates.

We have improved the sonic spray interface to enable the analysis of multiply charged ions of protein from a solution at a flow rate of 1 mL/min using a conventional liquid chromatograph/mass spectrometer. In this interface, we added a multihole plate in front of the sampling orifice of a mass spectrometer. This plate does not have a hole coaxial to the sampling orifice but has small holes around the central region of the plate. The plate reduces the density of the solvent molecules in the sprayed gas introduced into the vacuum region through the sampling orifice from the atmosphere and prevents the ions from being solvated and becoming charged droplets due to the cooling that follows adiabatic expansion of the sprayed gas. With this improvement, multiply charged ions whose charge distribution ranged from 11+ to 16+ were analyzed from a 1 μM cytochrome c solution at a high flow rate of 1 mL/min without using a splitter.

Multiply-charged Ion Formation by Sonic Spray

In sonic spray ionization technique, a solution from a fused-silica capillary is sprayed with a sonic gas flow coaxial to the capillary. The current for the ions produced and for the charged droplets is found to be dramatically enhanced when a voltage is applied to a surrounding metal piece, which is isolated from the solution by the fused-silica capillary. This can be ascribed to the induced concentration difference between positive and negative ions in the solution near the surface. Furthermore, multiply-protonated molecules produced in this way from protein solutions are analyzed with a quadrupole mass spectrometer. The ion intensity shows a strong dependence on the voltage but the diameter of the droplet produced by the spray is likely to be independent of the voltage. Thus, we conclude that the charge density of the droplet is regulated by the voltage.

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.

Multi-atmospheric pressure ionisation interface for liquid chromatography-mass spectrometry

We describe the structure of a multi-atmospheric pressure ionisation (multi-API) interface for liquid chromatography-mass spectrometry (LC-MS). This interface includes five modes of atmospheric pressure spray with electron impact ionisation (APEI), atmospheric pressure chemical ionisation (APCI), atmospheric pressure spray ionisation (APSI), electrospray ionisation (ESI) and sonic spray ionisation (SSI). This LC-MS system was realised by developing an APEI interface which resembles other API interfaces and a highly sensitive API interface using advanced collision induced dissociation in a differential pumping region and an electrostatic ion guide. This system can deal with a wide variety of organic compounds from hydrocarbons with low polarity to proteins with high polarity by using the five modes.

Use of water cluster detector for preventing drunk and drowsy driving

Implementing safety measures to prevent drunk and drowsy driving is a major technical challenge for the car industry. We have developed a system that involves a non-contact breath sensor to do this. The breath sensor detects breath by measuring electric currents of positively or negatively charged water clusters in breath that are separated by using an electric field. Our device couples a breath sensor with an alcohol sensor, and simultaneously detects the electrical signals of both breath and alcohol in the breath. This ensures that the sample is from a persons breath, not an artificial source. Furthermore, our breath sensor can detect breath from about 50 cm, and can also test the level of alertness of a subject sitting in the drivers seat. This is done by measuring the point of time the breathing changes from conscious, such as in pursed-lip breathing, to unconscious when the driver becomes drowsy. This is the first time that one device has been used to detect both drunk and drowsy driving.

RECENT PROGRESS IN ATMOSPHERIC PRESSURE IONIZATION MASS SPECTROMETRY

Abstract Atmospheric pressure ionization (API) is used as an interface in liquid chromatography-mass spectrometry and capillary electrophoresis-mass spectrometry. In API, quasi-molecular ions of biological molecules in solution are produced at atmospheric pressure. There have recently been several significant advances in spray ionization techniques, which use a solution spraying process. This article gives an overview of three spray ionization techniques: electrospray, ion spray, and sonic spray. It presents their characteristic features and describes the ion formation processes from charged droplets. Furthermore, the charged droplet formation process for each technique is described in terms of the non-uniformity in positive and negative ions in solution as well as in terms of the atomization process.

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.

Water-Cluster-Detecting Breath Sensor and Applications in Cars for Detecting Drunk or Drowsy Driving

Developing safety measures to prevent drunk and drowsy driving is a major technical challenge for the car industry. I have developed a system for this that involves the water-cluster-detecting (WDC) breath sensor. The WCD breath sensor detects breath by measuring electric currents of positively or negatively charged water clusters in breath that are separated by using an electric field. The WCD breath-alcohol sensor couples the WCD breath sensor with an alcohol sensor and simultaneously detects the electrical signals of both breath and alcohol in the breath. This ensures that the sample is from a persons breath, not an artificial source. Furthermore, the WCD breath sensor can detect breath from about 50 cm and can also test the level of alertness of a subject sitting in the drivers seat of a car. This is done by measuring the point of time at which the breathing changes from conscious, such as in pursed-lip breathing, to unconscious, such as when the driver becomes drowsy. This is the first result that one device has been used to detect both drunk and drowsy driving.

Electrostatic ion guide using double cylindrical electrode for atmospheric pressure ionization mass spectrometry

A novel electrostatic ion focusing lens that consists of two cylindrical electrodes positioned coaxially with each other is described. Square openings are formed in the inner electrode and their angular positions alternate by 90° with respect to the neighboring openings in the axial direction. When a potential difference is applied between the inner and outer electrodes, an electric field penetrates into the interior of the inner electrode through the openings. In the capillary electrophoresis/mass spectrometry analysis of peptides, use of the lens makes it possible to apply a higher voltage to the postacceleration dynode and the signal to background ratio is improved by a factor of 7.