Abstract:
A method for studying a fluid by forming a stream of the fluid, exciting the stream by causing a laser beam to impinge thereon to produce secondary particles or quanta, and subjecting the resulting secondary particles or quanta to an analysis operation in an analyzer.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of application Ser. No. 82,603, filed Oct. 9, 1979 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to the analysis of fluids, including liquids or mixtures thereof. 
     There are a number of known methods for analyzing gases or liquids. However, all these methods have limited sensitivity. The expenditures required to increase sensitivity increase considerably, with the increase in sensitivity, as is true for many measuring methods. 
     One way to analyze gases is to ionize the gases in an electron surge ion source and to then perform the analysis proper with the aid of a mass spectrometer, e.g. a quadrupole mass spectrometer. In such a method gases to be examined unavoidably come into contact with the structural elements of the ion source, where they are precipitated. This is a drawback not only because it causes corrosion of the structural components, but particularly also because it gives rise to effects due to prior contaminations which falsify later measurements. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to eliminate such drawbacks from a method of the above-mentioned type. 
     This and other objects are achieved, according to the present invention by exciting a stream of fluid to be analyzed by means of a laser beam and utilizing, in a known manner, the resulting secondary particles or quanta for the analysis proper. The fluid stream can travel freely in space in the region where the laser beam impinges thereon so that no other components need be located there which could produce &#34;memory&#34; effects. 
     The laser beam is capable of producing a strong excitation of the fluid stream so that, for example, the ionization probability is very high. Due to the free flow of the fluid stream, there is no problem in arranging the entrance opening of an analysis device in optimum proximity to the point of intersection of the laser beam with the fluid stream. This enables the present invention to attain an extremely high sensitivity. 
     It is particularly advisable to subject the ions created during bombardment of the fluid stream to a mass analysis employing a time of flight mass spectrometer, known per se. This measure has the result that the analysis result will be available very quickly. 
     Further advantages, offered by the present invention, are: that the fluid stream can be injected with the aid of a nozzle into a vacuum chamber in such quantities that no significant deterioration of the vacuum in the chamber occurs; that the laser light which is directed approximately perpendicularly to the exit direction of the fluid can be focused on a point disposed immediately downstream of the exit opening of the nozzle; and that the entrance opening of the analyzer can be arranged at an optimum distance from the point of intersection of the laser beam with the fluid stream. A pulsed laser beam as well as a fluid stream pulsed in approximately the same rhythm can be used for this purpose. This contributes to minimizing the quantity of fluid flowing into the vacuum chamber. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1, 2, and 3 are cross-sectional, detail views of three preferred embodiments of an apparatus for practicing the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1 and 2 both show part of a vacuum chamber 1 which includes an essentially tubular section 2 and a cover flange 3 for closing the frontal face opening of section 2. The cover flange 3 is provided with a cover glass 4 which is transparent to laser light and is set into flange 3 in a vacuum tight manner. On the outside of this cover glass 4 there rests a lens system 5 which acts to focus, or concentrate, a collimated laser beam 6 at a point 7 in the interior of the vacuum chamber. The device for generating the laser beam is not shown and can be constituted by any suitable known laser light source. The time of flight tube 8 of a known time of flight mass spectrometer is disposed within the vacuum chamber 1 in such a manner that the laser beam 6 and the illustrated section of the time of flight tube 8 have a common axis 9. Advisably, an ion optical system may be placed upstream of the time of flight tube 8; however, to better depict the contribution of the invention, this is not shown here. 
     In the embodiment of FIG. 1, an inlet tube 10 extends through the cover flange 3 and has a nozzle opening 11 in the vicinity of the focal point, or point of convergence, 7 of the laser beam. The fluid to be examined is introduced into the vacuum chamber 1 through this inlet tube in such a manner that the focal point 7 of the laser beam falls within the fluid stream. The desired ions are generated by bombarding the fluid stream with a pulsed laser beam and are then analyzed with the aid of the time of flight mass spectrometer of which tube 8 forms a part. 
     In the embodiment of FIG. 1, the mass rate at which fluid to be examined can be introduced must be limited to a value which will not substantially impair the vacuum. 
     In the embodiment of FIG. 2, the opening 12 of a suction pipe 13 is disposed in line with the nozzle end 11 of the inlet tube 10, which has here been brought through a side wall of section 2. The fluid carrying members are arranged so that the focal point 7 of the laser beam lies between the nozzle 11 and the opening 12. In this embodiment, a relatively strong fluid stream can be provided without impairing the vacuum since the fluid stream is removed directly from the vacuum chamber 1 through tube 13. Tubes 10 and 13 are arranged in such a manner that the fluid stream to be examined travels approximately perpendicularly to the axis 9 of the analyzing system. 
     FIG. 3 shows the arrangement of an ion optical system between the focal point 7 of the laser beam and the entrance of the time of flight tube 8. This ion optical system consists of a pulse electrode 20 and three electrodes 21, 22 and 23 forming an immersion particle lens. The mountings and connections for the power supply as well as the power supply itself have been omitted for purposes of clarity. The electric field between electrodes 20 and 21 accelerates the particles towards the mass spectrometer 8, which can be constituted by a device sold under the designation Lamma 500 by Leybold-Heraeus GmbH, Cologne, Federal Republic of Germany. The electrodes 20, 21, 22 and 23 serve for collimation of the particles produced at the laser focus 7. All potentials of the elements 10, 13, 20, 21, 22. 23 and 8 can be chosen for a proper performance of the instrument. The inserts 24, 25 and 26 serve as insulators. To evacuate the vacuum chamber 1, a flange 27 connectable to a commercial vacuum pump is provided. 
     It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.