Along with worsening international conflictions, detection apparatus for detecting explosives have been demanded for preventing terrorism or keeping security. As the detection apparatus, security check apparatus using X-ray transmission have been used generally including airports. X-ray detection apparatus recognize a target as a lump and judge a dangerous target based on the information for the shape and the like thereof and this is referred to as bulk detection. On the other hand, a detection method based on gas analysis is referred to as trace detection, which identifies the substance based on the information of chemical analysis. The trace detection has a feature capable of detecting a trace amount of ingredients deposited on a bag, etc. In view of the a social demand for strict security check, it has been demanded for an apparatus in combination of bulk detection and trace detection thereby capable of detecting dangerous target at a higher accuracy.
On the other hand, for finding illicit drugs carried on various routes, the detection apparatus are used, for example, also in the custom office or the like. While the bulk detection apparatus and drug detecting dogs are mainly used in the custom offices, it has been keenly demanded for a trace analysis apparatus for use in absolute drugs instead of drug-sniffing dogs.
For trace detection, various analysis methods such as ion mobility spectroscopy and gas chromatography have been attempted. Research and development have been under progress for the apparatus having high speed, sensitivity together and selectivity which are important for the detection apparatus.
In view of the situations described above, since mass spectroscopy is basically excellent in the speed, the sensitivity and the selectivity, a detection technique based, for example, on the mass spectroscopy has been proposed (refer to Patent Document 1 (JP-A No. 134970/1995): prior art 1).
FIG. 9 is a view showing the constitution of a dangerous target detection apparatus of the prior art 1. The existent detection apparatus based on the mass spectroscopy is to be described with reference to FIG. 9. An air intake probe 1 is connected by way of an insulative pipe 2 to an ion source 3, and the ion source 3 is connected by way of an exhaust port 4 and an insulative pipe 5 to a pump 6 for use in air exhaustion. The ion source 3 comprises a needle electrode 7, a first aperture electrode 8, an intermediate pressure section 9 and a second aperture electrode 10. The needle electrode 7 is connected with a power source 11. The first aperture electrode 8 and the second aperture electrode 10 are connected with an ion acceleration power source 12. The intermediate pressure section 9 is connected by way of an exhaust port 13 with a vacuum pump, not shown. An electrostatic lens 14 is located subsequent to the intermediate pressure section 9, and a mass analysis section 15 and a detector 16 are disposed subsequent to the electrostatic lens 14. A detection signal from the detector 16 is supplied through an amplifier 17 to a data processing section 18.
The data processing section 18 judges plural m/z (ion mass number/ion valence number) values showing a specified chemical and judges whether the specified chemical is contained or not in a gas to be tested. The data processing section 18 comprises a mass judging section 101, a chemical A judging section 102, a chemical B judging section 103, a chemical C judging section 104 and an alarm driving section 105. Further, display sections 106, 107 and 108 are disposed to an alarm display section 19 driven by the alarm driving section 105.
Further, for monitoring chemical substances, it has been known a method of conducting tandem mass analysis simultaneously in case where plural species of molecules to be measured present (refer to Patent Document 2 (JP-A No. 162189/2000): prior art 2).
Further, in a method of leaving aimed ions in the inside of an ion trap mass spectrometer while discharging other ions, a method of applying a signal having different amplitudes depending on frequencies between end gap electrodes has been known (refer to Patent Document 3 (U.S. Pat. No. 5,654,542): prior art 3).
Further, it has been known a method of deflecting and converging ions by a double cylindrical deflector comprising an inner cylindrical electrode and an outer cylindrical electrode (refer to Patent Document 4 (JP-A No. 85834/1995): prior art 4).
Further, a mass analysis method using filtered noise fields has also been known (refer to Patent Document 5 (U.S. Pat. No. 5,206,507): prior art 5).
The detection apparatus described in the prior art 1 involves the following problems. In the detection apparatus described in the prior art 1, a drug is judged by using an m/z value of an ion generated from the ion source. Accordingly, in a case where a chemical substance generating an ion having an identical m/z value with that of the chemical as a target of detection is present, it has a high possibility of causing erroneous information of indicating alarm irrespective of the absence of the drug to be detected.
More specifically, during detection of a stimulant drug in a luggage, the apparatus reacts to the components of cosmetics contained in the luggage to generate erroneous information. This is attributable to that the selectivity of the mass spectrometric section for analyzing ions is low and it cannot distinguish the ion derived from the stimulant and the ion derived from the cosmetics that incidentally has an identical m/z value.
As method of enhancing the selectivity in the mass spectrometer, a tandem mass analysis method has been known, a triple quadrupole mass spectrometer or a quadrupole ion trap mass spectrometer has been used for an apparatus to practice the tandem mass analysis. In the tandem mass analysis method, the following steps (1) to (4) have usually been used.
(1) First Step Mass Analysis:
Mass analysis is conducted to measure m/z for ions generated from an ion source.
(2) Selection:
An ion having a specified m/z value is selected from the ions having various m/z.
(3) Dissociation:
Selected ion (precursor ion) is dissociated by collision with a neutral gas or the like to generate an ion decomposition product (fragment ion).
(4) Second Step Mass Analysis:
In a case where the precursor ion is dissociated, it depends on the strength of chemical bonds of each site. Accordingly, when the fragment ion is analyzed, a mass spectrum highly abound in molecular structure information of the precursor ion is obtained. Accordingly, even when the ions generated from the ion source incidentally have identical m/z, the target to be detected can be distinguished by checking the mass spectrum of the fragment ions and it can be judged more exactly where the target to be inspected is contained or not.
Accordingly, in the detection apparatus of the prior art 1 shown in FIG. 9, when the mass spectrometric section 15 is replaced with a triple quadrupole ion trap mass spectrometer or quadrupole ion trap mass spectrometer and the tandem mass analysis method is conducted, it can be expected for the development of a detection apparatus capable of improving the selectivity and decreasing the occurrence of erroneous information. However, since the tandem pass analysis method takes a more time compared with usual mass analysis methods, it brings about a new subject that a detection speed required for the detection apparatus cannot be obtained.
With the reasons described above, it has been demanded for a detection apparatus having both high selectivity and high detection speed.
In the tandem mass analysis, when the technique described in the prior art 2 of dissociating plural ions simultaneously is applied, it can be expected for the development of a detection apparatus having both high selectivity and high detection speed but it brings about the following problems.
For example, in a case of detecting explosives, chemical properties of explosives as the target for detection, for example, easiness of dissociation and molecular weight are versatile. Then, more deliberate care is necessary compared with a case of simultaneously measuring only the targets having easiness of dissociation and molecular weight such as chrolophenols and dioxines. For example, when plural explosives are dissociated under identical conditions, since the efficiency of the dissociation changes greatly on every explosives, it results in a problem that a specific explosive cannot be detected effectively.
Further, for obtaining good detection result with less erroneous information, it is necessary to finely set the amplitude of a high frequency applied to the end gap also in a case of selecting plural ions. This is because some explosives are dissociated already in the course of selection. A device as described in the prior art 3 of applying a greater amplitude for a lower frequency was not yet sufficient.