Abstract:
In one embodiment, an analytical apparatus is provided that includes a carriage; and a plurality of electrospray probes pivotably mounted on the carriage, wherein movement of the carriage engages a feature with a selected one of the electrospray probes whereby movement of the feature pivots the selected one of the electrospray probes with respect to the carriage.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority to International Application PCT/US05/058303, filed Feb. 23, 2005, which in turn claims the benefit of U.S. Provisional Application No. 60/547,281, filed Feb. 23, 2004, the contents of both of which are incorporated by reference. 
     
    
     TECHNICAL FIELD  
       [0002]     The present invention relates generally to chemical analysis, and more particularly to an electrospray probe interface for mass spectrometry.  
       BACKGROUND  
       [0003]     Automated systems for measuring the concentration of analytes in a sample have been developed using a number of analytical techniques such as chromatography or mass spectrometry. In particular, mass spectrometry is often the technique of choice to achieve sensitivity of parts per billion (ppb) or sub-ppb such as parts per trillion (ppt). For example, co-assigned U.S. Ser. No. 10/004,627 (the &#39;627 application) discloses an automated analytical apparatus measuring contaminants which may be present in trace concentrations or constituents which may be present in substantial concentrations using a form of In-Process Mass Spectrometry (IPMS).  
         [0004]     In an IPMS technique, a sample of interest is spiked, i.e., has added to it a known amount of the appropriate isotopic species or an internal standard. After the spike and sample have equilibrated, the mixture is ionized using an atmospheric pressure ionization (API) technique such as electrospray and processed in a mass spectrometer to determine a ratio measurement. Depending upon the composition of the spike, the ratio will either be an altered isotopic ratio as used in isotope dilution mass spectrometer (IDMS) or the ratio of an internal standard to the analyte of interest. Unlike the harsh ionization using in inductively coupled mass spectrometry (ICP-MS), the mild ionization provided by the use of API enables the characterization of complex molecules rather than just elemental species. Because a ratio measurement is used, the analysis is immune to drift and other such inaccuracies that plague conventional mass spectrometry analyses.  
         [0005]     The IPMS technique represents a dramatic improvement over conventional mass spectrometry methods. Whereas conventional mass spectrometry methods require considerable hands-on intervention from highly-trained analytical chemists, IPMS is completely automated. Because of this automation, IPMS may be used to characterize analytes in fields such as semiconductor clean rooms where the use of mass spectrometry would traditionally be inappropriate. Moreover, this automation may be used to characterize virtually any type of analyte one may be interested in—from elemental species (which may be mono-isotopic) to complex molecular species. However, this automation faces a bottleneck at an electrospray probe used for electrospray ionization. Before a new analysis may be completed, the electrospray probe must be rinsed and then conditioned with the newly-equilibrated spike/sample solution. Having been conditioned, the probe may be used in the characterization of an analyte of interested in the newly-equilibrated spike/sample solution. This delay complicates the analysis of, for example, a copper plating solution in a semiconductor bath in which a user may desire to know the concentrations of a number of plating accelerants, retardants, constituents, and contaminants. To measure each one of these analytes thus entails an appreciable amount of delay because of the associated rinse and conditioning cycles.  
         [0006]     Accordingly, there is another need in the art for an improved IPMS apparatus that reduces the delay associated with repetitive rinse and conditioning cycles.  
       SUMMARY  
       [0007]     In accordance with the present invention, an analytical apparatus includes: a carriage; and a plurality of electrospray probes pivotably mounted on the carriage, wherein movement of the carriage engages a feature with a selected one of the electrospray probes whereby movement of the feature pivots the selected one of the electrospray probes with respect to the carriage.  
         [0008]     In accordance with another aspect of the invention, a method of using an electrospray assembly including a plurality of electrospray probes mounted on a carriage includes the acts of: conditioning a selected one of the electrospray probes; moving the carriage such that a feature engages the selected one of the electrospray probes; and moving the feature such that the selected one of the electrospray probes pivots into a mass spectrometer bore.  
         [0009]     In accordance with another aspect of the invention, an analytical apparatus is provided that includes: a plurality of electrospray probes; means for moving the plurality of electrospray probes such that a selected one of the electrospray probes is positioned with respect to an mass spectrometer bore; and means for moving the selected one of the electrospray probes into the mass spectrometer bore. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1   a  is a perspective rear view of an assembly of electrospray probes in accordance with an embodiment of the invention.  
         [0011]      FIG. 1   b  is a close-up view, partially cutaway, of the needle portion of the electrospray probes of  FIG. 1   a.    
         [0012]      FIG. 2  is a perspective rear view of the assembly of  FIG. 1   a  mounted onto the door of a mass spectrometer.  
         [0013]      FIG. 3   a  is a perspective view of a single electrospray probe in accordance with an embodiment of the invention.  
         [0014]      FIG. 3   b  is a cross-sectional view of a portion of the probe of  FIG. 3   a.    
         [0015]      FIG. 4  is a perspective front view of the assembly of  FIG. 3 .  
         [0016]      FIG. 5  is a block diagram of an automated mass spectrometry system in accordance with an embodiment of the invention. 
     
    
       [0017]     Use of the same reference symbols in different figures indicates similar or identical items.  
       DETAILED DESCRIPTION  
       [0018]     The present invention provides an electrospray probe assembly that eliminates the delay associated with rinsing and conditioning an electrospray probe used for repetitive analyses. Turning now to the Figures, a rear isometric view of an exemplary electrospray assembly  50  is illustrated in  FIG. 1   a . A plurality of electrospray probes  100  are mounted within a carriage assembly  110 . Assembly  110  mounts through a bore  115  onto a shaft (described below). Depending upon the linear displacement of carriage assembly  110  with respect to the shaft, a feature on the shaft (also described below) engages a desired probe  100 . Because of this engagement, as the shaft rotates, a conditioned probe  100   a  is pivoted into an entry orifice  200  of a mass spectrometer (for illustration clarity, only a door  203  of the mass spectrometer is illustrated) as seen in  FIG. 2 . Conditioned probe  100   a  may then provide an ionized sample to the mass spectrometer. In  FIG. 2 , carriage  110  is shown mounted through bore  115  on an outer shaft (element  205 ). A linear actuator  220  may be used to displace carriage  110  along shaft  205 . Similarly, a rotary actuator such as a pneumatic rotary actuator  230  may be used to rotate a probe  100  into entry orifice  200 .  
         [0019]     An isolated electrospray probe  100  is shown in  FIG. 3   a . As seen in the cross-sectional view in  FIG. 3   b , probe  100  includes a liquid inlet  300  in communication with a needle inside of a bore  305 . Also in ultimate communication with bore  305  is a nebulizing gas inlet  310 . Flexible tubing (not illustrated) couples to inlets  300  and  310  to allow for movement of probe  100 . Through liquid inlet  300  and associated tubing, probe  100  may receive ultra pure water (UPW) or other suitable cleaning fluid for rinsing between samples. In addition, probe  100  may also receive samples through liquid inlet  300  for conditioning and testing purposes. Referring back to  FIG. 2 , note the advantages of this arrangement. While conditioned probe  100   a  is providing its sample to the mass spectrometer through entry orifice  200 , other probes such as a probe  100   b  may be rinsed with UPW and conditioned with the sample to be tested. In this fashion, after conditioned probe  100   a  has finished providing its sample to the mass spectrometer, it may be rotated back into the inactive position so that assembly  110  can be moved along shaft  205  to position another conditioned probe into entry orifice  200 . Thus, the conditioning and rinsing of probes  100  introduces no delay in the analysis performed by the mass spectrometer.  
         [0020]     As seen in  FIG. 3   a , probe  100  may include a probe block  330  including a feature so that probe  100  may be engaged and pivoted into entry orifice  200  of the mass spectrometer ( FIG. 2 ). In this exemplary embodiment, the feature comprises a notch  340 . Turning now to  FIG. 4 , a key  400  may be rotated by rotary actuator  230  to engage notch  340  and pivot the selected probe. As seen in  FIG. 4 , assembly  110  mounts through threaded adapter  410  onto a jackscrew  420 . Outer shaft  205  may thus be hollow to receive jackscrew  420 . As linear actuator  220  ( FIG. 2 ) rotates jackscrew  420 , assembly  110  displaces along outer shaft  205  to engage a conditioned probe with key  400 . Rotary actuator  230  may drive an inner shaft  420  to rotate key  400 . Rotation of inner shaft may be limited by a stop (not illustrated). Thus, the position of the stop would determine the angle at which the conditioned probe projects into entry orifice  200 . By adjusting the position of the stop, the projection angle of the conditioned probe may be adjusted accordingly.  
         [0021]     Each probe  100  may be grounded through a corresponding ground contact  440 , which should be resilient to accommodate pivoting of the corresponding probe. It will be appreciated that another potential besides ground may be achieved through appropriate biasing of ground contact  440 . As seen in  FIG. 1   a , counter electrodes  120  for the probes may be mounted in a rack  130 . Turning now to  FIG. 1   b , a close-up of a needle portion  150  for each probe  100  is shown. The height of counter electrodes  120  with respect to rack  130  may be adjusted using a screw  160 . In addition, a contact  170  may be provided to maintain electrical contact between rack  130  and counter electrodes  120  despite the mobility of counter electrodes  120 . For illustration clarity, only a single needle portion  150  is shown in cross-section. As seen in  FIG. 2 , a ground plane  270  may shield counter electrodes  120  from the probe  100   a , which is pivoted through mass spectrometer entry orifice  200 . To accommodate this pivoting, ground plane  270  may be notched as shown.  
         [0022]     Although the electrospray assembly described with respect to  FIGS. 1   a  through  4  may be advantageously used with conventional mass spectrometers, it also enhances the use of the automated mass spectrometer disclosed in U.S. Ser. No. 10/004,627. A block diagram overview of an embodiment of such an automated mass spectrometer system incorporating the electrospray assembly disclosed herein is shown in  FIG. 5 . A sample extraction, dilution, and spiking module  500  is adapted to extract a sample and spike the extracted sample. If necessary, either the sample, the spike, or the equilibrated spike/sample mixture may be diluted. The type of spike depends upon the analyte being characterized in the sample. Certain analytes such as Cu are amenable to isotopic dilution analysis such that the spike would be a known amount of Cu having an altered isotopic ratio. Other analytes such as complex molecules are not as amenable to an isotope dilution mass spectrometer (IDMS) analysis because it would be too expensive to synthesize a complex molecule having an altered isotopic ratio. Alternatively, certain analytes such as Co are virtually monoisotopic such that there is no isotopic ratio to alter. In such a case an internal standard type of analysis may be performed as will be explained further herein. Regardless of whether an IDMS or internal standard analysis is being performed, module  500  mixes the spike and sample and allows the mixture to equilibrate before delivering the mixture to electrospray interface  510 .  
         [0023]     Interface  510  may be constructed as discussed with respect to  FIGS. 1   a  through  4 . To provide a rinsing solution, electrospray interface  510  may receive UPW from a UPW source  520 . Electrospray interface  510  ionizes the spike/sample mixture received from extraction module  500  so that the ions may be characterized by a mass spectrometer  520 . As discussed analogously with respect to  FIG. 2 , while a conditioned probe is providing its ions to the mass spectrometer, additional probes may be rinsed (from source  520 ) and conditioned with sample/spike mixture from extraction module  500 .  
         [0024]     Mass spectrometer measure a response for both the sample and the spike. By forming a ratio of these responses, the concentration of the analyte in the sample may be characterized. Advantageously, this ratio will cancel out instrument drift and other inaccuracies, thereby providing precision and accuracy. Moreover, the ratio method just described is independent of whether an internal standard or IDMS method is utilized. Should an internal standard be used as the spike, it need merely have a sufficiently similar chemical behavior through assembly  510  and mass spectrometer  520 .  
         [0025]     Processor  530  controls the configuration of module  500  and electroprobe interface  510  to maintain an automated operation. For example, processor  530  would control actuators  220  and  230  of  FIG. 2  as necessary.  
         [0026]     The above-described embodiments of the present invention are merely meant to be illustrative and not limiting. For example, rather than linearly displace probes  100  with respect to shaft  420  so that key  400  engages a conditioned probe  100   a , these probes may be arranged on a wheel in a semi-circular arrangement. By rotating the wheel, a selected probe may be engaged with a feature that pivots the selected probe into a mass spectrometer entry orifice. It will thus be obvious to those skilled in the art that various changes and modifications may be made without departing from this invention in its broader aspects. Accordingly, the appended claims encompass all such changes and modifications as fall within the true spirit and scope of this invention.