Laser microprobe interface for a mass spectrometer

Details Laser microprobe interface for a mass spectrometer Laser microprobe interface for a mass spectrometer

1990-05-04

1992-05-26

Anderson, Bruce C.

Radiant energy

Ionic separation or analysis

With sample supply means

250423P, B01D 5944, H01J 4940

Patent

active

051171082

DESCRIPTION:

BRIEF SUMMARY
The present invention concerns a laser microprobe interface for a mass spectrometer, such as a Fourier transform mass spectrometer featuring a cell holder which holds a double cell--source cell and analysis cell--situated at the core of a superconductor magnet, the ions being generated within the source cell by means of electron impact, preferably perpendicular on the introduced samples, before being analyzed there at means pressure, therefore at low resolution, and then transferred through an orifice in a conducting plate into the axis of a magnetic and temporarily charged field, called, into the analysis cell where they are analyzed at very low pressure, therefore at very high spectral resolution, the interface itself principally composed of, firstly, focusing optics and visualizing optics, secondly, of an optical stage which allows for the introduction and adjustment of laser rays as well as for the visualization of the samples and, finally, of a system for the introduction of the samples.
Actually, laser microprobe interfaces for time of flight mass spectrometers are already known, both in the transmission configuration, such as those known commercially as LAMMA 500 and manufactured by the LEYBOLD-HERAEUS company, and in the reflection configuration, such as those commercially known as LAMMA 1000 and manufactured by the LEYBOLD-HERAEUS company. We also know of laser microprobe interfaces having a transmission and reflection configuration, such as those commercially known as LIMA and manufactured by the CAMBRIDGE MASS SPECTROMETRY Company, Ltd.
These interfaces offer the advantage of good sensitivity and good spatial resolution, and allow for good reproduction and rapidity of measurement.
However, they have the major disadvantage of only allowing for a limited spectral resolution. Actually, since the interval of the total time between two ions is less than a nanosecond, this exceeds the capabilities of the most rapid transitory recording devices presently existing on the market.
Therefore we have conceived laser microprobe interfaces for use with a Fourier transform mass spectrometer, which allows for operation in a highly pressurized vacuum, and offers a very high spectral resolution. However, since the ions must be generated within the magnetic field, the major problem is that of being able to take advantage of an almost perfect vacuum in the analyzing cell, which is to say a vacuum on the order of 10.sup.-9 torr, in order to increase the life of the ions to be analyzed, so that after the Fourier transformation of the interferogram (image current that, amplified, forms the detection signal), a mass spectrum with a high spectral resolution is obtained, with the difference in mass ##EQU1## between two ions separated at 10% from the well (height of the peak) having to be larger than 100,000.
In an initial device, the double cell of the mass spectrometer using the Fourier transformation is separated by a semi-sealing conducting metallic wall, penetrated by a small orifice, this allowing, firstly, for the transfer of ions from the source cell to the analysis cell, secondly, ensuring a differential vacuum between the two cells on the order of 10.sup.2 torr, which is to say, 10.sup.-7 for the source cell, and 10.sup.-9 for the analysis cell, and finally allowing for trapping of the ions in one or the other of the two cells by adequately adjusting the potential.
In this way, a high spectral resolution is obtained, as well as good focusing at 90.degree. in relation to the sample (therefore a perfectly circular impact), and ease in handling the sample. In this device, however, sample visualization must be ensured by an endoscope. Now, since an endoscope cannot magnify an image more than 10 times, the result is a very low image definition. It is understood that it would be possible to visualize the sample using the same optics that are used to focus the laser rays. However, given the focal length of the lens having a diameter of 110 mm, and the maximum magnification of a telescope which is on the order of 25 tim

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"Laser Descorption Fourier Transform Ion Cyclotron Resonance Mass Spectrory vs Fast Atom Bombardment Magnetic Sector Mass Spectrometry for Drug Analysis", Shomo et al., Anal. Chem., vol. 57, pp. 2940-2944, No. 14, Dec. 1985.
H. Vogt, et al., "Lamma 500 Principle and Technical Description of the Instrument," Fresenius Z. Anal. Chem., vol. 308, pp. 195-200, 1981.

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