JPS5819849A - Mass spectrometer - Google Patents

Abstract

PURPOSE:To improve total sensitivity and reduce differential sensitivity due to mass by properly applying optional voltage to an opening plate which restricts an ion beam on the ion exit side end of a quadrupole. CONSTITUTION:Voltage is applied properly to an opening plate P for restricting an ion beam so as to form an electric field in the direction where an ion is accelerated between the ion beam restricting opening plate P located on the ion exit side end of a quadrupole QP and the electrode end of the QP. This opening plate P is connected to a variable voltage power supply V. The specified mass number ion proceeds in the arrow direction, passes through an open A, and is incident on an ion detector FC. When a positive ion is handled, the ion which passes between the QP electrodes is absorbed in the opening plate P by applying negative voltage to the opening plate P, accelerated, and passes through the QP end edge. As a result, sensitivity is improved and differential sensitivity can be reduced due to mass.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a quadruple species mass spectrometer. In a quadruple seed mass spectrometer, ions of a specific mass that have passed between the quadrupole (hereinafter abbreviated as Q and P) in a stable orbit also pass through the edge electric field formed at the end of the QP. The cross-section of the ion beam is broadened, which leads to decreased sensitivity in quadruple-species mass spectrometers, mass discrimination (sensitivity decreases as the mass increases), and a broadened peak profile in the mass spectrum. This has an adverse effect such as a decrease in mass selection effect. The present invention was made with the aim of reducing the above-mentioned adverse effects of the edge electric field of QP.

The magnitude of the influence that the edge field of QP has on ions depends on the time required for the ions to pass through the edge field, and the longer this time, the greater the influence from the edge field. The time t that an ion stays in the edge field is expressed by the length of the edge field, the mass of the L1 ion as M, and the kinetic energy of the ion as E. According to equation (1), it is predicted that if the kinetic energy of the ion is large, the residence time of the ion in the edge field will be reduced, and the influence of the edge field will be reduced. Usually, the kinetic energy of an ion is determined by the accelerating voltage when the ion is introduced into the QP electric field. The present invention provides a suitable aperture plate for forming an electric field in the direction of accelerating the ion beam between the ion beam limiting aperture plate provided at the end of the ion exit side of the QP and the electrode end of the QP. The present invention provides a mass spectrometer that applies voltage.

By doing this, by adding the increase in kinetic energy due to the electric field between the QP electrode end and the aperture plate to the kinetic energy given when the ions are introduced into the QP electric field, the right side of the above equation (1) can be expressed. By increasing E, the influence of the edge field is reduced.

←The figure shows the main part of one embodiment of the present invention, R1 and R2 are Q
A pair of P electrode rods are shown, P is an aperture plate, A is an aperture for limiting the ion beam, and FC is an ion detector.

The aperture plate P is connected to a variable voltage power supply V. Ions of a specific mass advance in the direction of the arrow in the figure, pass through the aperture A, and enter the ion detector FC. When dealing with positive ions, when a negative voltage is applied to the aperture plate P, the ions that have passed between the QP electrodes are attracted to the aperture plate P, so they are accelerated and pass through the edge field of the QP. Therefore, as the voltage of the aperture plate P increases from the ground to the negative side, the influence of the edge field decreases and the ion detection output increases. The table below compares the change in ion transmittance of the mass spectrometer as a whole when the aperture plate P is grounded and when a negative voltage is applied for two types of positive ions.

m: mass 2: amount of charge (in electron units) As seen from the above table, the effect of applying an ion acceleration voltage to the aperture plate is particularly remarkable for ions, which are the dog of mass, and it not only improves the overall sensitivity but also reduces the sensitivity difference due to mass. You can also get the effect of reducing the size.

[Brief explanation of the drawing]

The drawing is a side view of a main part of an apparatus according to an embodiment of the present invention. R1, R2...Q, P electrode rod, P... aperture plate, A.
...Ion beam limiting aperture, FC...Ion detector, ■...Variable voltage power supply. Agent Patent Attorney Kosuke Agata

Claims (1)

[Claims] A quadruple seed mass spectrometer in which an arbitrary voltage can be applied to the aperture plate that limits the ion beam at the ion exit end of the quadrupole.