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.

To detect vapors from explosives, we have developed a new detection system based on a novel ion source for atmospheric pressure chemical ionization (APCI). The direction of the sample gas flow introduced into the ion source is opposite to that of the ion flow produced by the ion source. We call this technique “counter‐flow introduction” (CFI). The CFI ion source has high ionization efficiency for nitro‐compounds and is installed in an ion‐trap mass spectrometer. Our tests on various military explosives show that this system is suitable for practical on‐line explosive detection; namely major explosives can be detected within a few seconds without any pretreatment of the sample gases.

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