WO1983003498A1

WO1983003498A1 - Mass-spectrometric method of analysis

Info

Publication number: WO1983003498A1
Application number: PCT/FI1982/000012
Authority: WO
Inventors: Tutkimuslaitos Oy Puumalaisen
Original assignee: Puumalainen, Pertti; Ikonen, Jorma
Priority date: 1982-03-31
Filing date: 1982-03-31
Publication date: 1983-10-13
Also published as: DE3249414T1; GB8331114D0; GB2128398A

Abstract

The ionization chamber (2) of the ion source of the mass spectrometer is constructed in normal manner, applying a sufficiently open geometry so that the chamber contamination caused by the sample might be reduced. This however entrains the drawback that comparatively large sample quantities are required because part of the sample is pumped out from the ionization chamber without being utilizable. The said conflict can be eliminated by applying the method of the invention, when the ion source is provided with a plurality of separate ionization chambers (2), of which whenever desired any one can be rapidly selected for use, without disturbing the vacuum or ion-optical conditions in the mass spectrometer. The method is particularly well applicable when employing a gas chromatograph as sample input unit (4) in analysis situations where the mass spectra of sample components succeeding each other rapidly are measured, or where it is desired to record low intensity mass peaks after the occurrence at the same mass numbers of very powerful mass peaks in the preceding sample component.

Description

Mass-spectrometric method of analysis

The present invention concerns a mass-spectrometric method of analysis wherein a plurality of samples are measured in succession by introducing the samples, one at a time, into an ionization chamher located hetween an entrance duct and the ion-optical system of a mass spectrometer. It is known in the art to employ in the ion source of a mass spectrometer a comparatively open ionization chamher which totally lacks for instance two opposed side walls. One avoids hereby even in rapid consecutive analyses the harmful hackground spectrum which results as a consequence of contamination of the ionization chamher by the preceding sample. However, the weak point of an ion source designed with open geometry is that the sensitivity of analysis suffers quite considerably because a large part of the molecules which should he analysed can escape from the ionization chamher into the vacuum volume surrounding it. Therefore, in constructing those ion sources which are being used at present it has always been necessary to seek a compromise between abundant contamination and sensitivity of analysis. This situation is particularly evident when using gas chromatographs with fast capillary columns for input units to introduce the mass spectrometer sample, in case the samples are small. In such gas chromato graph/mass spectrometer combinations the sample components enter the ionization chamher at intervals even as short as 10 seconds.

The object of the present invention is to accomplish a procedure for carrying out rapid consecutive analyses wherein the ionization chamber of the ion source is as closed as possible during analysis, to the purpose of achieving added sensitivity of analysis, and where this same chamber on the other hand is as pure as possible from contamination caused by the preceding sample when another analysis commences, whereby the interference of the background spectrum from contamination with the analysis is minimized.

The features which are characteristic of the procedure of the invention are set forth in the claims. The invention is described in greater detail in the following with the aid of an example, referring to the attached drawing, wherein:-

Fig. 1 presents the ionization chamher of a mass spectrometer with entrance duct, and the ion-optical system of the mass spectrometer, and

Figs 2-8 present parts of the disk-like member constituting the ionization chambers, as follows:-

Fig. 2 showing the topmost part of the disk-like member, in top view,

Fig. 5 showing the part of Fig. 2 in elevational view,

Fig. 4 showing the middle part of the disk-like member, in top view,

Fig. 5 showing the part of Fig. 4, in section and in elevational view,

Fig. 6 shows the lowermost part of the disk-like member in top view,

Fig. 7 shows the part of Fig. 6, from below, and

Fig. 8 shows the part of Fig. 6, sectioned and in elevational view.

Fig. 1 depicts, in section, a rotating, disk-like member 1 comprising four separate ionization chambers 2. To the disk-like member 1 has been connected a vacuum-protected shaft 3 controllable from outside the mass spectrometer: by rotating this axle, any one of the ionization chambers 2 can he placed in register with the end of the entrance duct 4 provided for the samples to be analysed. On one side of the disk-like member 1 an electron-emitting incandescent filament 5 has been mounted, and the other end of the shaft 3, electrically insulated from the ionization chamher system, serves as collector for the electron beam. The system required for elec tron guidance has been indicated in Fig. 1 with the reference numeral 6 and the ion-optical system of the mass spectrometer, with 7.

The disk-like member 1 presented in Fig. 1 has been assembled of three separate parts of stainless steel, Figs 2-8 clarifying the design of these parts. The topmost part 8, depicted in Figs 2 and

3, has for exiting ions four slits 9, located radially so that the angle hetween each two slits is 90º. The middle part 10, depicted in Figs 4 and 5, comprises five apertures so that in the aperture in the centre, 11, is affixed the shaft 3 rotating the chambers 2, the rest of the apertures constituting the interior spaces of the chambers. The part 10 is furthermore provided with holes 13 for entrance and exit of electrons ionizing the sample molecules. The lowermost part 14, depicted in Figs 6-8, comprises an aperture 15 for the shaft 3 and four sample entrance holes 16. The holes 16 are located on the bottom of a groove 17 in the underside of the part

14, and the end of the sample entrance duct 4 is disposed in this groove, as can be seen from Fig. 1. The parts 8, 10 and 14 are hound together in the member 1 by means of rivets.

In the method of analysis of the invention, samples to be measured are introduced, one at a time, through the duct 4 into the ionization chamber 2 located in register with the duct end. Between each two consecutive measurements, a change of ionization chamber 2 is performed by turning the shaft 3, whereby the chamber used in measuring the preceding sample moves to be cleaned in the vacuum space of the mass spectrometer and a new, clean chamber Is provided for the measuring of the next sample. The interference effect of the contamination from the preceding sample is thereby eliminated, and thus it becomes possible by this procedure to measure samples following in quick succession after each other, or such samples from which low intensity mass peaks are measured after mass peaks of high intensity have occurred at the same mass numbers in the preceding sample.

The sample input duct 4 depicted in Fig. 1 may consist of a gas chromatograph, in which case the measurements and changes of ionization chamber 2 are undertaken in accordance with the fractioning of the sample material into components to be measured which takes place in the gas chromatograph apparatus.

It has been possible by means of an ion source operating according to the principle here disclosed, to improve the sensitivities of analysis by one order of magnitude, compared with conventional ion sources. Moreover, the harmful background has been kept in the analyses nearly on the same level on which it was when the first sample component arrived in the mass spectrometer.

Claims

1. Mass-spectrometric method of analysis wherein a plurality of samples is measured in succession by introducing the samples one at a time into an ionization chamber (2) located between a sample entrance duct (4) and the ion-optical system (7) of a mass spectrometer, characterized in that in the method is employed a plurality of ionization chambers (2) which are movable and of which any one can he placed between the sample entrance duct (4) and the ion-optical system (7), and that between measurements on consecutive samples a change of ionization chambers is effected, whereby for measuring the new sample a clean chamber is obtained, while at the same time the chamber used in the measurement of the preceding sample moves to become cleaned, into a vacuum space provided in the mass spectrometer.

2. Method according to claim 1 , characterized in that the ionization chambers have been disposed in a rotatable disk-like member (1) provided with a vacuum-protected shaft (3) controllable from outside the mass spectrometer so that the change of ionization chamher hetween measurements takes place by turning the shaft.

3. Method according to claim 1 or 2, characterized in that as sample entrance duct (4) is employed a gas chromatograph and that the measurements and changes of ionization chamber (2) are performed in accordance with the fractioning of the sample material into components to be measured taking place in the chromatograph.