the basic matters of the one - dimensional ion trap according to this invention are explained with reference to a first embodiment . a second embodiment deals with the form of operation using the one - dimensional ion trap according to this invention as a mass spectrometric analysis means . in a third embodiment , the form of operation using the one - dimensional ion trap according to this invention as an ion mobility means is explained . this embodiment deals with the basic matters of the one - dimensional ion trap including a solid - cylindrical electrode ( inner electrode ) formed of a solid cylinder and a hollow - cylindrical electrode ( outer electrode ) formed of a hollow cylinder . the electrode structure includes the hollow - cylindrical electrode 1 ( radius : r 2 ) and the solid - cylindrical electrode ( radius : r 1 ) arranged on the same axis . a radio frequency voltage ( amplitude vrf , frequency ω / 2π ) is applied to the solid - cylindrical electrode using a radio frequency voltage power supply 3 , where the dc bias of the rf voltage should be zero , while a dc voltage ( udc ) is applied to the hollow - cylindrical electrode using a dc voltage power supply 4 , where the rf voltage of the dc voltage should be zero . the aforementioned arrangement in terms of voltage is shown in fig1 . first , the motion of ions with the electrode arrangement and voltage described above is theoretically described . the potential formed between the two electrodes is dependent on the distance r from the center axis and given by the equation below . upon application of this potential , the potential for generating the force acting on ions in time average is given as the calculation of this equation employs the pseudo - potential method generally used in the radio frequency ion trap theory . this equation is formed of two parts on the right side including the first term representing the pseudo - potential due to the radio frequency and the second term the potential due to the electrostatic voltage . this is illustrated in fig2 . specifically , the pseudo - potential applies the outward force from the center axis to the ions and has no effect on the polarity of the ions . the electrostatic voltage , on the other hand , is adapted to apply the force toward the center axis to the ions . the dc voltage udc is positive in the case where positive ions are trapped , and negative in the case where negative ions are trapped . the potential equal to the sum of the two potentials , i . e . the potential given by equation ( 2 ) is also shown in fig2 . as understood from fig2 , the potential of the one - dimensional ion trap according to this invention has a local minimum value , and from equation ( 2 ), the position assuming the particular local minimum value is given by equation ( 3 ) below . in order to obtain the local minimum value , the polarity of udc is of course required to be determined with respect to the polarity of ions as described above . from equation ( 3 ), it is understood that ions having a large m / z value are located inside near the center axis and ions having a small m / z value outside far from the center axis . in this way , with the one - dimensional ion trap according to this embodiment , it is understood that ions having different m / z values are trapped cylindrically at different radii . for this reason , this method is called the one - dimensional trap . the range of m / z value in which ions can be trapped is determined by the values of the radio frequency voltage and the electrostatic voltage . in other words , ions that can be trapped have a stable area unique thereto . this fact is derived from the condition that “ there must exist a stable point of ions given by equation ( 3 ) between inner and outer electrodes ; otherwise , ions would bombard the electrodes ”. specifically , the relation holds that the condition that the solid - cylindrical electrode is not bombarded by ions leads to equation ( 5 ). also , the condition that the hollow - cylindrical electrode is not bombarded by ions leads to equation ( 6 ). the ions existing within the area determined by these two values are actually trapped . based on this principle , an explanation is made in more detail according to the actual electrode size and voltage condition . the values described below are used as representative parameters to be substituted . using these values of the device parameters , the value m / z = 13 - 1325 is obtained as a range of the mass in which ions can be trapped . this ion trap is considered applicable to various environmental pollution substances , illegal drugs and hazardous objects . in these applications , however , the valence number z of ions often assumes unity , and therefore , ions having the molecular weight of about 13 to 1300 can be trapped . this range covers the molecular weight of all the molecules to be detected in these applications . the ion trapping process along the direction of the center axis is explained . as described in “ summary of the invention ” above , this invention discloses two means for trapping ions in the direction along the center axis . ( 1 ) disk - shaped wall electrodes are arranged at the two ends and the ion leakage is prevented by applying a dc voltage ( fig3 a ) ( 2 ) wall electrodes conducting with the hollow - cylindrical electrode are added to short the electrode ends . as a result , the rf voltage is deformed , and an ion converging force is generated as a pseudo - potential ( fig3 b ). according to the means ( 1 ) above , ions are trapped by applying a dc electric field to the wall electrodes by a dc voltage . in the means ( 2 ), on the other hand , the electromagnetic wave due to rf can be prevented from leaking out of the electrodes , and as compared with the means ( 1 ), the number of parts is reduced , thereby providing a method that can be implemented at low cost . fig4 a and 4b show the potential determined by numerically calculating the potential applied in the form of the electrode shown in fig3 b and calculating the pseudo - potential as in equation ( 2 ). the potential depth is indicated by the color density so that the color higher in density indicates a deep potential and the color lower in density a low potential . the calculation uses the representative device parameters described above . it is understood from fig4 a that the bottom of the potential is separated from the end portion and that the potential for trapping ions is formed also in the direction of the center axis . it has been found , however , that with the decrease in m / z , the bottom of the potential is formed on the electrode and ions are lost as shown in fig4 b . this indicates that with the decrease in m / z , the outward potential due to radio frequency is increased and overcomes the inward force due to the electrostatic voltage , resulting in the loss of ions . especially at the corner making up the bottom of the potential , the electric field is weak and the effect is great . after all , it has been found that this method can trap ions in the direction along the center axis but the mass area is somewhat reduced on the low mass side . this reduction , however , is very small and the effect thereof is considered substantially ignorable in application . to summarize , the method according to this embodiment has the great features described below . ( 1 ) ions are converged on the surface of a cylinder having the radius given by equation ( 3 ). in the conventional three - dimensional trap ( what is called the paul trap ), on the other hand , ions are converged at one point . also , in the conventional two - dimensional trap ( what is called the linear ion trap ), ions are converged on a straight line . ( 2 ) ions different in m / z are converged on the surfaces of cylinders different in radius . according to the paul trap , on the other hand , ions having different m / z values are converged at the same point . also , in the conventional linear ion trap , ions having different m / z values are converged on the same straight line . these two features of the one - dimensional trap according to this invention makes it possible to reduce the mutual interaction between a plurality of ions and the spatial charge effect , as compared with the conventional methods , in an application to the mass spectrometry as described in the second embodiment . sample ions are most simply introduced from a hole formed in the hollow - cylindrical electrode . the ion trap according to this embodiment can be set to the vacuum degree of 1 torr ( 0 . 01 pa ) which can be easily realized by what is called the roughing vacuum pump ( the low vacuum pump such as the rotary pump or the diaphragm pump , the turbo molecular pump for realizing a high vacuum may not be used ). in this case , the relation between vacuum degree and viscous resistance is such that the value of a typical ion mobility k is 0 . 8 to 2 . 4 cm ̂ 2 / v / sec ( for 14 to 500 amu @ ambient pressure ). fig5 shows the result of calculating the trajectory of ions introduced from the hollow - cylindrical electrode under the conditions specified by “ ion mobility spectrometry ”, g . a . eicemann & amp ; z . karpas , crc press . 2005 . in fig5 , ( 1 ) designates a case in which m / z is 20 , ( 2 ) a case in which m / z is 200 , ( 3 ) a case in which m / z is 1000 , and ( 4 ) a case in which m / z is 1500 . with the ion trajectory in equilibrium , the radius at which ions are located is equal to the value given by equation ( 3 ). in the case of ( 4 ) above , however , the conditions are unstable , and therefore , ions are lost by bombarding the electrodes . according to this calculation , ions are introduced at the rate of not more than 1 ms . specifically , according to this method , ions are settled in about 1 ms , and therefore , a high - speed operation is made possible . incidentally , the trajectory for m / z = 20 appears thick due to the forced vibration ( what is called the micromotion ) caused by radio frequency . a large micromotion blurs the position of ions and has an adverse effect on the mass resolution in mass spectrometry applications . the micromotion can be effectively reduced by increasing the radio frequency and reducing the value udc . according to this embodiment , the frequency of not lower than 2 mhz is determined as a proper value . ions can be introduced still faster by increasing vrf and udc and thus deepening the potential not to change the stable ion position . as seen from equations ( 3 ), ( 5 ) and ( 6 ), the shape of the potential remains unchanged by holding the relation vrf ̂ 2 ∝ udc . incidentally , ions having a specified m / z can also be isolated by use of equations ( 3 ) and ( 4 ) in the one - dimensional ion trap according to this embodiment . specifically , in accordance with the m / z value of target ions , the radio frequency voltage or the electrostatic voltage is changed thereby to approach the stability boundary m 1 ( heavy side ) or m 2 ( light side ). with the approach to m 1 , a large m / z value is excluded , while the approach to m 2 eliminates ions having a small m / z value . although the two stability boundaries cannot be approached at the same time , ions can be isolated by combining the two operations . the isolation resolution can be determined by the degree to which the m / z value of the target ions can approach a stability boundary . an application of the one - dimensional ion trap as an analysis means is described . this application is based on the principle defined by equations ( 3 ) and ( 4 ) for determining a stable area according to the first embodiment . specifically , the instability in the trap conditions is utilized as a mass spectrometric analysis method . as described in summary of the invention above , stable ions trapped are instabilized ( i . e . instabilized in mass selectivity ) by controlling and changing the voltage condition , and the electron current generated by bombarding the electrode is measured by the ampere meter . in this way , the m / z value and the quantity of the trapped ions are measured . this operation has the feature that the mass spectrometry conducted using the static stability conditions of ions makes possible the analysis independent of the gas pressure . specifically , the operation is possible in low vacuum . the term “ low vacuum ” is generally defined as about 1 to 10 − 6 torr , while the term “ high vacuum ” about 10 − 6 to 10 − 8 torr . in the conventional method of mass spectrometric analysis operation , the resonance vibration of ions is utilized , and therefore , the bombardment of the gas has so large an effect on the resolution that the low - vacuum operation is impossible and a high vacuum is required . for carrying out the mass spectrometry using the one - dimensional ion trap according to this embodiment , two ion detection methods described below are available . ( a ) the ion current is measured by mass selective bombardment of ions against the solid - cylindrical electrode . ( b ) the ion current is measured by mass selective bombardment of ions against the hollow - cylindrical electrode . also , for carrying out the mass spectrometry using the one - dimensional ion trap according to this embodiment , three mass selective scanning methods described below are available . from these choices , six combinations are basically conceivable , and the superiority of any one of them over the others can be determined using the degree of the mass resolution as an index . according to this embodiment , the combinations of ( a ), ( b ) with ( 1 )( 2 ) are studied below . the parameters described above are used for calculations . in the case of ( 3 ), the mass selective scanning is made possible by scanning the frequency of the digital wave while maintaining a constant amplitude . as to the criterion for superiority , a high mass resolution can be most easily achieved in the case where a linear result is obtained on a graph plotting a variable parameter along the abscissa and the mass at the stability - instability boundary along the ordinate . thus , a case producing a substantially linear relation is selected . the calculation result is shown in fig6 a and 6b . fig6 a shows the calculation result in the case where ions are detected by scanning the radio frequency amplitude . the line designated by a 1 indicates the m / z value with ions bombarding the solid - cylindrical electrode 2 and the line designated by a 2 the m / z value with ions bombarding the hollow - cylindrical electrode 1 . the ions existing in the area defined by the two lines are stably trapped , while ions existing in other than this stable area bombard the solid - cylindrical electrode or the hollow - cylindrical electrode and fail to be trapped in stable condition . also , fig6 b shows the calculation result in the case where the electrostatic voltage is scanned to detect ions . the line designated by b 1 represents the m / z value with ions bombarding the solid - cylindrical electrode 2 and the line designated by b 2 the m / z value with ions bombarding the hollow - cylindrical electrode 1 . the ions existing in the area defined by the two lines are stably trapped , while the ions existing in other than this stable area bombard the solid - cylindrical electrode or the hollow - cylindrical electrode and fail to be trapped in stable condition . as indicated by line a 1 , the calculation result for a method to detect the ion current with the solid - cylindrical electrode ( inner electrode ) while scanning the radio frequency amplitude due to this line is substantially linear and considered easy to detect . the mass spectrometric analysis operation is basically possible also by other methods . line a 2 represents a case in which the radio frequency amplitude is scanned to detect ions with the hollow - cylindrical electrode ( outer electrode ). the case is also applicable , though narrow in the mass range in which instability increases with respect to the scanning amount of the radio frequency amplitude . line b 1 represents a case in which the dc voltage is scanned to detect ions on the solid - cylindrical electrode . in this case , though applicable for detection , a slight voltage change in the high mass area greatly changes an unstable area , and therefore , a high resolution cannot be easily achieved with a high mass . further , line b 2 represents a case in which the dc voltage is scanned and the ion current is detected on the hollow - cylindrical electrode . also this case , though difficult to achieve a high resolution , is applicable in spite of the fact that a slight parameter change results in a great change in unstable mass . as described above , all the operation methods can basically produce a mass spectrum . from the viewpoint of the ease with which a resolution is easily secured , however , the method indicated by line a 1 in which the radio frequency amplitude is scanned and ions are detected on the solid - cylindrical electrode ( inner electrode ) is considered the best embodiment . also , the method indicated by line b 1 in which the electrostatic voltage is scanned to detect ions on the solid - cylindrical electrode ( inner electrode ) is considered the next best embodiment . a system configuration for embodying the principle described above is shown in fig7 . the ion trap portion includes a hollow - cylindrical electrode 1 , a solid - cylindrical electrode 2 , insulating members 7 , 8 for isolating the two electrodes from each other and supporting the solid - cylindrical electrode 2 , a vacuum bath 9 for accommodating these trap electrodes , a vacuum pump 10 , an ion source 11 and a pipe 12 for introducing the ions generated in the ion source to the vacuum bath . the radio frequency power supply 3 shown in fig1 includes such elements as a oscillator 15 , a multiplier 17 , a radio frequency amplifier 18 , a step - up radio frequency transformer 19 , a rf amplitude monitor circuit 20 , capacitors 21 , 22 and a feedback amplifier 16 . the current monitor circuit includes a current amplifier 23 . the radio frequency amplitude and the electrostatic voltage are controlled and the current value read by a digital / analog converter 14 controlled by a computer 13 . incidentally , the vacuum pump 10 is a diaphragm pump . now , the circuit parts are explained . the radio frequency amplitude control voltage generated by the converter 14 in response to a command from the computer 13 is multiplied by the signal of the oscillator 15 through the feedback amplifier 16 , and the amplitude - controlled radio frequency signal is input to the radio frequency amplifier 18 . the power - amplified radio frequency signal is further amplified by the transformer 19 and input to the solid - cylindrical electrode 2 . the amplitude of the voltage at the output end of the transformer 19 is converted into a low electrostatic voltage and input to the feedback amplifier 16 . this circuit , makings up a negative feedback circuit , is controlled in such a manner that the output voltage of the transformer 19 is always proportional to the control voltage output from the converter 14 . incidentally , the output signal of the oscillator 15 may assume a rectangular wave or , more preferably , a sinusoidal wave . this is by reason of the fact that the transformer 19 and the ion trap electrode make up a resonance circuit and only the resonant sinusoidal wave component is amplified , so that the voltage applied to the ion trap actually assumes a sinusoidal wave . the voltage generated by the converter 14 is input as an electrostatic voltage to the hollow - cylindrical electrode 1 . in the process , the transformer 19 is connected using the capacitors 21 , 22 so that the radio frequency power may not pass through the converter 14 , while at the same time inserting an electric resistance ( about 1 mω ) connected with the converter 14 as required . as a result , the radio frequency power locally exists between the transformer and the trap electrode . the ion current follows the route from the solid - cylindrical electrode 2 through the transformer to the current amplifier 23 . the output of the current amplifier is analyzed by the computer through the converter 14 . the a 1 mode described above is most preferable as an analysis process . the radio frequency amplitude is set to a value as large as about 200 v and the ions generated by the ion source are trapped . about one millisecond later , the ions enter an equilibrium state , and therefore , the radio frequency amplitude is scanned downward . then , the outward force due to the radio frequency is reduced and the ions move toward the center . once the ions bombard the electrode , the ion quantity is detected as an ion current . as described above , by measuring the ion current with respect to the radio frequency amplitude , a mass spectrum can be obtained . the radio frequency amplitude is converted to the m / z value of ions according to equation ( 3 ). an application of the invention to an ion mobility analysis means is explained . a system configuration is similar to that of the second embodiment . first , the mass analysis operation ( second embodiment ) is performed to determine the m / z value of target ions . then , the ion species is isolated by the method described in the first embodiment . the isolated ions are set to a high voltage at a radio frequency amplitude to locate it in the neighborhood of the outside of the ion trap to lengthen the drift distance . then , the voltage vrf is turned off instantaneously , and ions having a large ion mobility k bombard the solid - cylindrical electrode before the remaining ions . the time difference between the time during which the radio frequency is turned off and the time when the ion current is measured indicates the ion mobility . by using this operation , the two - dimensional measurement of the mass - to - charge ratio and the ion mobility of the specimen ions is made possible . also , the ion mobility can be measured by detecting the current on the hollow - cylindrical electrode with the electrostatic voltage instantaneously turned off . fig8 shows two calculation results for 50 % different values of the ion mobility k . in this case , the ion m / z value is 200 and the electrostatic voltage of 1 v is applied . the trajectory shown in ( 1 ) is 50 % larger in ion mobility than the trajectory shown in ( 2 ). in this way , the time before reaching the surface of the solid - cylindrical electrode ( indicated by dotted line ) is varied with k , and therefore , ions different in mobility in spite of the same m / z value can be distinguished . it should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention , the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims .