Patent Publication Number: US-8536522-B2

Title: Mass spectrometer

Description:
The present invention relates to the field of mass spectrometry. 
     BACKGROUND ART 
     Mass spectrometers are expensive instruments that can be used for the analysis of many different types of analytes. In order to analyse some of these analytes, different methods of ionisation may be required. 
     It would therefore be useful for a user to be able to switch quickly and easily between different types of ion sources as and when they are required. However, different types of ionisation techniques may require rather different conditions or parts. Therefore, it would be useful to have easily attachable and removable sources for the different ionisation techniques so that users can simply, and quickly change the way they ionise their samples in a safe and secure manner. A further advantage to this is that during maintenance, if any failure has occurred in the source, a new source enclosure may be fitted to reduce downtime of the instrument in question. 
     In many cases, samples may be run with potentially dangerous chemicals as solvents. For example, most LC methods utilise acetonitrile or methanol, which are heated in the MS source to form toxic vapours. If a source enclosure is detached so that another source enclosure can be placed upon the instrument, it may therefore be extremely important to provide an air tight seal between the ion source chamber and the laboratory. Therefore, it is very important that the source can be tested upon mounting to the instrument so that any leaks that may be present between the source chamber and the laboratory can be identified before the instrument is allowed to intake sample, thus stopping any potential leakage of dangerous chemicals. 
     When in use, failures in the exhaust systems of the mass spectrometer may cause a dangerously over pressurized source. Therefore, a continued diagnostic analysis of the source to recognize any blockages before they raise the pressure to a dangerous level would be desirable. 
     If the exhaust system is at a pressure above that of the ion source chamber, a backflow may occur from the exhaust into the mass spectrometer. This may cause interferences in the results of the system, or if the source is unlocked at the time, this may cause the laboratory to be contaminated with potentially hazardous chemicals. Therefore, an additional back flow prevention means would also be desirable so that this condition can be avoided. 
     Therefore, a new, easily detachable and reattachable ion source with all the above features would be desirable. 
     SUMMARY OF THE INVENTION 
     The invention provides a detachable and replaceable ion source for a mass spectrometer having a mass spectrometer mounting for detachably receiving said ion source, the ion source comprising a housing which defines an ion source chamber, an ion source mounting means complementary to said mass spectrometer mounting to detachably couple with said mass spectrometer and to allow movement of the housing to bring the ion source chamber into a position of use at the inlet of said mass spectrometer and to take the ion source chamber from said position of use into a retracted position, sealing means to create a air tight seal between said housing and said mass spectrometer when the ion source chamber is in said position of use, and a release mechanism that cooperates with said mass spectrometer to allow said movement of said housing. 
     According to a feature of the invention the ion source mounting and the complementary mass spectrometer mounting may together allow pivotal movement of the ion source housing towards and away from the inlet of said mass spectrometer. Preferably, the ion source mounting and the complementary mass spectrometer mounting together allow translatory movement of the ion source housing when in the retracted position in a direction along the axis of said pivotal movement to allow detachment and replacement of the ion source housing with respect to said inlet of the mass spectrometer. 
     According to another feature of the invention, pressure sensor means may be provided to allow continuous monitoring of source pressure and periodic leak checking of the source enclosure and wherein the pressure sensor means may be adapted to actuate a pressure check valve to prevent potentially dangerous source over-pressurization occurring in fault conditions. Preferably, the pressure sensor means is operatively connected to an atmospheric pressure ionization (API) solenoid which is adapted to close at a predetermined pressure to protect the pressure sensor means. Preferably, an exhaust isolation valve is provided and operative in the event that API gas is not present to prevent migration of external gases into the ion source. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various embodiments of the present invention will now be described, by way of example only, and with reference to the accompanying drawings in which: 
         FIG. 1  shows a partially detached source enclosure in the vicinity of the mass spectrometer in accordance with the invention; 
         FIG. 2  shows an attached source enclosure fitted to the mass spectrometer; 
         FIG. 3  shows a view of the source form the side at which it fits on to the mass spectrometer; 
         FIG. 4  is a schematic diagram of a system incorporating an ion source and a mass spectrometer, according to the invention; and 
         FIG. 5  illustrates a seal which seals between the ion source enclosure and the inlet of the mass spectrometer. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  is a diagram of an ion source in accordance with the current invention. The source ( 1 ) is hinged away from, and thus retracted from, but proximal to, the mass spectrometer ( 3 ). The ion source detachably latches on to the mass spectrometer by a complementary latch mechanism ( 5 ) on the mass spectrometer and release mechanism ( 7 ) upon the ion source housing. The release handle ( 9 ) actuates release mechanism  7  so as to release the ion source from the mass spectrometer when in a closed position of use so that it can be hinged into the retracted position as shown. 
     The source may be mounted on the mass spectrometer by way of mounting points ( 11  and  13 ) and corresponding mounting cavities (not shown) upon the source at a mounting plate ( 15 ). The mounting plate is hingably attached to the main source body by a plurality of hinges ( 17  and  19 ). A seal ( 21 ) seals the ion source to the mass spectrometer so that the source enclosure ( 23 ) is sealed in an air tight manner. 
       FIG. 2  shows the ion source in an attached position of use, such that it is sealed to the mass spectrometer. In order to release the ion source, the user removes the inlet connections from the mass spectrometer ( 25 ). Once these connections have been removed, the release handle ( 9 ) is pulled outwards in order to release the source from the latch on the mass spectrometer. 
       FIG. 3  shows the ion source from the side at which it fits on to the mass spectrometer. The mounting cavities ( 27 ) upon the mounting plate ( 15 ) are arranged such that upon attachment to the mounting points, the source enclosure is securely fitted to the instrument. In order for the source to be detached from the mounting points the source must be lifted off the mounting points upon the mass spectrometer. Thus the ion source housing is moved in a direction along the axis of its pivotal connection when in its open, retracted position. 
     Referring now also to  FIG. 4 , every time the user closes the source enclosure or inserts a probe the source is briefly pressurized to test for leaks. Desolvation gas is injected into the ion source chamber through value  27  and the pressure in the chamber is monitored by means of a pressure sensor  29 . If the pressure of the source chamber drops significantly the test (a leak test) would be failed. If the test result is a fail the user is warned or otherwise prevented from using the source in a potentially unsafe condition. The test takes about 30 seconds to complete. 
     The leak test may be initiated automatically, 5 seconds after the source is closed or the probe is inserted or manually. If the leak test fails, a prominent message warns the user. 
     The source enclosure pressure sensor  29  allows continuous monitoring of source pressure and periodic leak checking. The pressure sensor will indicate excessive pressure caused by blocked or partially blocked exhausts. 
     A pressure check valve  31  prevents potentially dangerous source over-pressurisation occurring in fault conditions. 
     The pressure sensor  29  is hardware interlocked to the API gas solenoid valve  27 , such that the API gas solenoid will close if the pressure exceeds 100 mbar in normal use, protecting the pressure sensor and the user. 
     The pressure warning at &gt;25 mbar will ensure low pressure exhaust systems are used, giving low source pressures and therefore reduced leakage rates in fault conditions. 
     When the API gas is switched off or in the event of API gas failure, an exhaust isolation valve  33  closes, preventing any migration of gases from the laboratory exhaust system into the source  1 . 
     The instrument exhaust is connected to the laboratory exhaust via a leak-tight union  35 . This prevents any possible leakage of source gases into the laboratory atmosphere if the laboratory exhaust system is inadequate, i.e. where the exhaust pressure exceeds atmospheric pressure. 
     Referring now to  FIG. 5 , the ion source incorporates a seal system  35  which provides an enhanced seal between the ion source chamber and the inlet of the mass spectrometer. 
     The seal  37  of seal system  35  has a deep seal profile which allows the seal to stay in place when the source is opened and closed. As can be seen the seal  37  has a substantially rectangular base  37   a  by which it is securely mounted in groove  39  of the ion source enclosure, and an arcuate domed exposed portion  37   b  which gives enhanced deformation. This seal profile depth gives a greater cross section of rubber, allowing a greater contact surface on the seal face and greater deformation of the seal. As the compression increases, the excess material spreads sideways to increase the contact land. The profile of the seal has also been made so that trapping of solvent/debris is reduced, the profile can easily be wiped clean for extended performance. Seals  37  are easily fitted by users, unlike conventional captive o-rings. 
     Other Embodiments 
     The invention gives a number of benefits including the protection of both source and exhaust system, a reduced risk of exposure to harmful solvent vapours, protection of MS system from contamination via laboratory exhaust and a system which is completely automated requiring no user intervention. 
     It will be apparent that various modifications may be made to the particular embodiments discussed above without departing from the scope of the invention.