Abstract:
The present invention provides methods and electronic circuits for a chemical analyzer, for example, a mass spectrometer, which provide generated signals that are maintained to a required level of precision. A user may specify the required precision for the signals which operate the spectrometer and may specify the required precision for the mass analysis, either explicitly or by choosing a predefined configuration. The spectrometer will then generate the signals to the required precision despite changes in operating conditions, environmental conditions, component aging and degradation, or other nonfailure effects that otherwise affect analyzer calibration and signal output. The electronic circuits incorporate signal monitoring to maintain closed-loop signal control. The closed-loop control includes a feedback path which may include discrete components and may include software enabling a processor to adjust the generated signals to maintain the required precision of the signals and analysis. Further, the spectrometer may monitor signals and analyze and store data in order to predict future performance, including precision, analysis limitations, impending component degradation or failure, or another parameter associated with a component or signal of the spectrometer. Specifically, a range for a particular parameter may be specified and a indication provided to a user when the parameter exceeds the specified range.

Description:
[0001]     This application claims the benefit of U.S. Provisional Patent Application No. 60/500,545 filed on Sep. 5, 2003. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates generally to the field of mass spectrometers and, more specifically, to mass spectrometers that include electronic control circuits for generating and adjusting electronic signals.  
         [0004]     2. Description of the Related Art  
         [0005]     A particular type of mass spectrometers, an ion trap, includes electrodes for analysis and subsequent detection and measurement of ions having various mass-to-charge ratios. The components of ion traps typically include two grounded end-cap electrodes sandwiching a ring electrode to which a radio frequency (RF) signal is applied for the trapping of ions, a filament and repeller for producing an electron beam, lens elements for ion focusing in order to transport ions or electrons, and an electron multiplier, channel plate, or other ion detector. Each of these components must be supplied with a highly precise direct current (DC), RF signal, or other waveform in order to perform the steps required for mass analysis of a chemical sample.  
         [0006]     There are many steps that are required to perform mass analysis of a sample. The sample must be acquired, transported to a mass spectrometer inlet, ionized, transported from the ionization region into the analyzer, mass analyzed, detected, digitized, and presented. Many of these steps require the precise generation of electronic signals which are also precisely biased and/or amplified to drive the above listed components of the mass spectrometer. For example, during and after ionization, the sample is manipulated with electric or magnetic fields or through fluid dynamics. The efficiency and accuracy of each of the analysis steps is dictated at least in part by the stability of the components that generate the electronic signals and resulting fields or flows. For the case of electronic field ion manipulation, the potential, frequency, and phase of signals driving the lens elements all can affect the motion of ions. Practical limitations to the electronic components used to generate the signals may cause enough inherent instability, imprecision, and degradation over time to affect the performance of the mass analysis.  
         [0007]     Typically, the user monitors the quality of the data and modifies the generated signals of the mass spectrometer in order to maintain optimum performance. However, signal calibration before analysis and periodic monitoring of the quality of the data may not allow the required precision and stability of the signals to be maintained. Additionally, a user may not detect component degradation over time that is suggestive of an impending failure of the component.  
         [0008]     What is needed in the art is a mass spectrometer that provides the required precision and stability of the signals. What is also needed in the art is a mass spectrometer that detects component degradation.  
       BRIEF SUMMARY OF THE INVENTION  
       [0009]     The present invention provides methods and electronic circuits for a chemical analyzer, for example, a mass spectrometer, which provide generated signals that are maintained to a required level of precision. A user may specify the required precision for the signals which operate the spectrometer and may specify the required precision for the mass analysis, either explicitly or by choosing a predefined configuration. The spectrometer will then generate the signals to the required precision despite changes in operating conditions, environmental conditions, component aging and degradation, or other nonfailure effects that otherwise affect analyzer calibration and signal output.  
         [0010]     The electronic circuits incorporate signal monitoring to maintain closed-loop signal control. The closed-loop control includes a feedback path which may include discrete components and may include software enabling a processor to adjust the generated signals to maintain the required precision of the signals and analysis. Further, the spectrometer may monitor signals and analyze and store data in order to predict future performance, including precision, analysis limitations, impending component degradation or failure, or another parameter associated with a component or signal of the spectrometer. Specifically, a range for a particular parameter may be specified and a indication provided to a user when the parameter exceeds the specified range.  
         [0011]     The inventive electronic circuits determine the actual signals that are applied, modify the signals passively to compensate for any instability, imprecision, or other discrepancies, digitize the signals and use active compensation to further modify the signals, and collect data concerning the signals, drift in the signals, and component, circuit, or other spectrometer performance to predict future performance. The inventive spectrometer can use all of the methods of potential correction or any subset thereof. The process may operate automatically and continuously.  
         [0012]     In one form, the present invention provides a method for controlling a signal in a mass spectrometer, including the steps of: providing a desired signal for controlling at least one of an ionization component and an analysis component of the mass spectrometer; at least one of amplifying and biasing the desired signal to produce an output signal; monitoring and storing data relating to the output signal; predicting a parameter relating to at least one of the output signal and the at least one of an ionization component and an analysis component, the predicting based on data stored in the monitoring and storing step; and providing an indication upon the parameter being outside of a range.  
         [0013]     In another form, the present invention provides a mass spectrometer including a signal generator capable of generating a desired signal; an electronic device receiving the desired signal and capable of producing an output signal based on at least one of amplifying and biasing the desired signal; a component configured to receive the output signal; a comparator receiving the desired signal and a feedback signal, the feedback signal being dependent upon the output signal, the comparator capable of producing an error signal as a function of the desired signal and the feedback signal; and a processor receiving the error signal and having software enabling the processor to analyze the error signal and determine future performance of the component, determine impending failure of the component, and/or modify the output signal or the desired signal.  
         [0014]     In yet another form, the present invention provides a mass spectrometer, including a component performing a mass spectrometry function; and a driving circuit electrically coupled to the component and driving the component, the driving circuit including a signal generator applying an output signal to the component; and a feedback device sensing at least one of a voltage and a current associated with the output signal and transmitting a feedback signal dependent thereon to the signal generator, wherein the signal generator modifies the output signal in order to maintain the at least one of a voltage and a current associated with the output signal within a range.  
         [0015]     An advantage of the present invention is that the mass spectrometer includes a circuit for controlling an output signal for a component. The circuit adjusts the output signal to achieve a required precision associated with the output signal. Thus, the accuracy of the mass analysis is increased and the requirement for initial and periodic manual calibration is reduced.  
         [0016]     Another advantage is that the mass spectrometer includes a circuit that monitors the output signal and predicts the level of precision that may be achieved and the likelihood of component or circuit degradation or impending failure of the component or circuit associated with the output signal. Thus, the reliability of the mass spectrometer may be monitored by the user. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of exemplary embodiments of the invention taken in conjunction with the accompanying drawings, wherein:  
         [0018]      FIG. 1  is a general block diagram of a functional assembly suitable for use in a mass spectrometer of the present invention;  
         [0019]      FIG. 2  is a block schematic diagram of a mass spectrometer according to the present invention including four particular embodiments of the functional assembly of  FIG. 1 ;  
         [0020]      FIG. 3  is a block schematic diagram of the filament circuit of the mass spectrometer of  FIG. 1 ;  
         [0021]      FIG. 4  is a block schematic diagram of the lens elements circuit of the mass spectrometer of  FIG. 1 ;  
         [0022]      FIG. 5  is a block schematic diagram of the ion trap RF electrode circuit of the mass spectrometer of  FIG. 1 ;  
         [0023]      FIG. 6  is a block schematic diagram of the electron multiplier circuit of the mass spectrometer of  FIG. 1 ;  
         [0024]      FIG. 7  is a flow diagram representing a method of calibrating the mass spectrometer of  FIG. 1 ;  
         [0025]      FIG. 8  is a flow diagram illustrating a first exemplary operating method associated with the mass spectrometer of  FIG. 1 ; and  
         [0026]      FIG. 9  is a flow diagram illustrating a second exemplary operating method associated with the mass spectrometer of  FIG. 1 . 
     
    
       [0027]     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate preferred embodiments of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.  
       DETAILED DESCRIPTION  
       [0028]     Referring now to the drawings, and particularly to  FIG. 1 , there is shown one embodiment of a functional assembly  10  suitable for use in a mass spectrometer of the present invention. Assembly  10  includes a component  11  for performing a mass spectrometry function, such as ionization, ion extraction, ion transportation, ion trapping, ion analysis, or ion detecting, for example. A driving circuit  12  is electrically coupled to and drives component  11 . Driving circuit  12  may include a signal generator  13 , including a signal processor  14  and an amplifier/biaser  15  for applying an output signal to component  11 . A feedback and sensing device  16  senses a voltage and/or a current associated with the output signal applied to component  11 . Device  16  then transmits a feedback signal dependent on the sensed voltage and/or current to signal generator  13 .  
         [0029]     The feedback signal may be amplified and/or scaled by amplifier/scaler  17  before being input to the signal processor  14 . Based on the received output from amplifier/scaler  17 , signal processor  14  may modify desired signal  19  such that the output signal applied to component  11 , i.e., the amplified/biased version of desired signal  19 , has an associated voltage and/or current within an acceptable range. That is signal generator  13  may modify the output signal in order to maintain a voltage, current, and/or other parameter associated with the output signal within a range.  
         [0030]     Referring now to  FIG. 2 , exemplary mass spectrometer  20  according to the present invention may include various control circuits for driving and monitoring mass spectrometer components. More particularly, spectrometer  20  includes four functional assemblies  10   a - d  for performing respective functions of mass spectrometry. Mass spectrometer  20  includes ionization region  21  having ionization components and analysis region  23  having analysis components. Filament  52  and repeller  54  and lens elements  82  are associated with ionization region  21 . Ion trap electrodes  26  and electron multiplier detector  112  are associated with analysis region  23 . Ionization can, in some instances, be performed in the ion analyzer, i.e., within analysis region  23 , rather than in an external volume such as ionization region  21 .  
         [0031]     Filament circuit  50  provides filament output signal  63  for driving filament  52  and repeller  54 . Filament  52  and repeller  54  produce an electron beam in ionization region  21  for ionization of the sample being analyzed. Filament circuit  50  may also receive filament monitor signal  65  for monitoring and/or providing feedback related to output signal  63  and aspects of filament  52  and repeller  54 .  
         [0032]     Lens elements circuit  80  provides lens output signal  91  to lens elements  82 . Lens elements  82  provide focusing of the ions generated by filament  52  and repeller  54  in order to extract and transport the ions from ionization region  21  to analysis region  23 . Lens element circuit  80  may also receive lens monitor signal  93  for monitoring and/or providing feedback related to output signal  91  and aspects of lens elements  82 .  
         [0033]     Ion trap RF electrode circuit  22  provides RF electrode output signal  25  for driving ion trap electrodes  26 . Electrode monitoring signal  39  may be received by electrode circuit  22  for monitoring and/or providing feedback related to output signal  25  and aspects of electrodes  26 . Ion trap electrodes  26  provides RF trapping of ions in order to hold ions in place in analysis region  23 .  
         [0034]     Electron multiplier circuit  110  provides multiplier output signal  121  to electron multiplier detector  112 . In addition to the feedback of signal  121 , the data collected by detector  112  may be used to alter parameters of other circuits, such as the lens signals, trap RF signals, and filament voltages. Electron multiplier detector  112  detects ions which have been transported from within the volume defined by ion trap electrodes  26  to the detector  112 . The ions are trapped within this volume confined by the electrodes, not on the electrodes themselves. In one embodiment (not shown), a conversion dynode is provided between ion trap electrodes  26  and detector  112 . The conversion dynode may function to boost gain and allow for detection of ions of either polarity. Electron multiplier circuit  10  may also receive multiplier monitor signal  123  for monitoring and/or providing feedback related to output signal  121  and aspects of electron multiplier detector  112 .  
         [0035]     For ion trap mass spectrometry, the sample or analyte is transferred from its native state, for example air, water, or solution, and is ionized in ionization region  21 . Referring to  FIG. 3 , filament  52  and repeller  54 , which is welded to an input end of filament  52 , produce an electron beam and a particular energy electron which impact molecules of the analyte to generate ions. The ionization process can be performed by many different types of ionization that vary based on the type of sample, the mass range of the analyte, and the statistical probability of collision. The ionization types may include, for example, electron impact ionization, chemical ionization, electron capture ionization, charge exchange, or other ionization sources known in the art of mass spectrometry.  
         [0036]     The performance and efficiency of all types of ionization relate to, at least in part, output signal  63 , i.e., the combination of signals  63 A and  63 B, which drives filament  52  and repeller  54 . The performance is also partially determined by the stability of the electronic system used to generate filament output signal  63 .  
         [0037]     In the case of electron impact ionization, the efficiency of the ionization process is determined by the accelerating potential that is imparted into the traveling electrons as well as the electron flux and ionization energy. The traveling electrons and electron flux are controlled by filament output signal  63  which is applied to repeller  54  behind discharging filament  52 , and the current flow from filament  52 , respectively. As the temperature of filament  52  and filament circuit  50  change, the performance also changes. Therefore, to ensure the most stable and precise mass analysis, continuous feedback regarding filament output signal  63  is desirable. Monitoring data may be used to adjust output signal  63 , and to predict one or more parameters such as future performance, filament lifetime, and fault conditions. For example, as current through filament  52  changes as a result of filament degradation, the likelihood of impending failure increases, indicating a decrease in the available filament lifetime.  
         [0038]     Referring still to  FIG. 3 , filament circuit  50  produces, monitors, and adjusts filament output signal  63 . Digital signal processor (DSP)  56  generates digital signal information that is provided to digital-to-analog converters (DACs)  58 A,  58 B. From the received digital signal data, DACs  58 A,  58 B produce desired filament signals  59 A,  59 B. Amplifier buffers  60 A,  60 B buffer desired signals  59 A,  59 B and couple the signals to filament bias  62 A and filament source  62 B, respectively.  
         [0039]     Filament bias  62 A provides voltage level control in order to provide the required DC bias of desired filament signal  59 A, thereby producing filament output signal  63 A. Filament output signal  63 A may be, for example, in the range of approximately 5 to 100 μAmps, while filament signal  63 B may be in the range of approximately 1 to 4 Amps. Filament signal  63 A provides a bias voltage for ejecting electrons from filament  52  which may be for example, from approximately −5 to −100 Volts, while filament signal  63 B from filament source  62 B provides power to heat filament  52 . Filament output signal  63  is coupled to filament  52  and repeller  54  which produce the electron beam and particular electron energy necessary for ionization.  
         [0040]     A current sense resistor  67 B may be electrically connected in series with the bias voltage applied to filament  52 . Feedback devices  71 A,  71 B may include voltmeters for sensing voltages associated with the output signal, such as voltages on opposite ends of resistors  67 A,  67 B. Moreover, from these sensed voltages, voltage drops across resistors  67 A,  67 B may be determined. From these voltage drops and the known resistances of resistors  67 A,  67 B, a level of current associated with filament  52  may be calculated. Feedback devices  71 A,  71 B generate feedback signals  72 A-D which may be indicative of any voltage and/or current associated with the output signal applied to filament  52 . In one embodiment, signal  72 A is indicative of emission current, signal  72 B is indicative of bias voltage, signal  72 C is indicative of filament current, and signal  72 D is indicative of filament voltage.  
         [0041]     Filament output signal  63 , and other output signals of mass spectrometer  20 , may be monitored using all or any of three methods and associated electronic components. First, filament output signal  63  may be measured. However, for some components of spectrometer  20 , the output signal is at a very high voltage and measurement may be difficult. Second, filament output signal  63  may be scaled, for example, by a voltage divider circuit, and then measured. Third, a comparison of feedback signals  72 B,  72 D after scaling may be made with desired signals  59 A,  59 B, respectively, thus providing filament error signals  73 A,  73 B.  
         [0042]     The advantages of monitoring output signal  63 , and other output signals of mass spectrometer  20 , include controlling output signal  63  to the desired amplitude or other desired parameter, and monitoring changes in output signal  63  which are associated with changes in aspects of circuit  50  and/or filament  52  (or the component associated with the output signal of interest). Specifically, for example, as filament  52  degrades over time, changes in the current flow through filament  52  to produce a specific emission current may be reflected in a change in the voltage amplitude of output signal  63 , thus requiring adjustment of output signal  63  and indicating degradation of filament  52 .  
         [0043]     The exemplary filament circuit  50  shown in  FIG. 3  provides amplifier buffers  64 A,  64 B for receiving feedback signals  72 A,  72 C and producing filament monitor signals  65 A,  65 B. Filament monitor signals  65 A,  65 B may be scaled, if required, by scaling devices  70 A,  70 B.  
         [0044]     Filament voltage signals  69 A,  69 B may be provided to amplifier buffers  60 A,  60 B, as shown in  FIG. 3 , or to filament bias  62 A and filament source  62 B, in order to provide passive control and adjustment of filament output signal  63 , thereby providing increased precision and stability of output signal  63  based on desired filament signals  59 A,  59 B.  
         [0045]     Advantageously, filament voltage signals  69 A,  69 B may be provided to DSP  56 , which may include hardware and/or software algorithms for monitoring, analysis, and adjustment of signals and for predicting future performance. Additionally, filament current signals  65 A,  65 B may be received by analog-to-digital converters (ADCs)  66 A,  66 B, which provide digital representations of filament monitor signals  65 A,  65 B to DSP  56 . By receiving filament current signals  65 A,  65 B and/or filament voltage signals  69 A,  69 B, DSP  56  may provide monitoring, analysis and adjustment of desired filament signals  59 A,  59 B in order to improve the performance and efficiency of circuit  50 , filament  52  and repeller  54 . Additionally, filament current signals  65 A,  65 B and/or filament voltage signals  69 A,  69 B may be monitored, analyzed and stored in order to evaluate instantaneous and trend performance and efficiency. Analysis of instantaneous and trend data allows DSP  56  to predict parameters such as the future performance of filament circuit  50 , filament  52 , and repeller  54 , including remaining lifetime, likelihood of impending failure, or other performance information.  
         [0046]     For example, DSP  56  may include software enabling DSP  56  to monitor, for example via output signal  63 , a level corresponding with a current flow through filament  52  and to adjust output signal  63  to achieve a desired current flow though filament  52  or electron emission current off of filament  52 . If the required adjustment of output signal  63  changes over time, DSP  56  may store the changes. A correlation between the stored changes over time versus the lifetime or some other parameter of filament  52  may be determined and stored by DSP  56  each time a change in output signal  63  is required, and the correlation and related information may be indicated to the user of mass spectrometer  20 . Additionally, if the monitored current flow is approximately zero, the failure of filament  52  is indicated to the user.  
         [0047]     Once the ions are generated, they may be extracted from ionization region  21  and transported to the analysis region  23 . Alternatively, the electrons may be transported from the filament into the analysis region where they may impact the sample and generate ions. In this case, the ions are not actually being extracted. Referring to  FIG. 4 , in exemplary mass spectrometer  20 , extraction transport is provided by lens elements  82 , which may be static (typically referred to as Einzel lenses) or dynamic (typically referred to as multipole ion guides). Lens output signal  91 , which is applied to lens element  82  electrodes, enables lens element  82  to focus the ions.  
         [0048]     Output signal  91  is an important factor in the efficiency of the transfer process, as drift of output signal  91  changes the focal point of lens element  82 . Additionally, for extraction and transport of ions, the bias of output signal  91  is established very accurately based on the mass of the ion, and therefore drift of output signal  91  may provide inaccurate focusing given the mass of the sample. Similarly to filament circuit  50 , lens element circuit  80  produces, monitors, and adjusts lens element output signal  91  in order to increase the precision and stability of output signal  91  and improve and predict future performance and efficiency of circuit  80  and lens element  82 .  
         [0049]     Specifically, DSP  56  may provide a digital representation of the desired signal to DAC  86 . DAC  86  produces desired lens element signal  87  which is coupled to an input of amplifier buffer  88 . The output of amplifier buffer  88  is coupled to the input of lens element bias  90 . Lens element bias  90  provides voltage level control in order to provide lens element output signal  91  in the range of, for example, −500 to 500 V DC.  
         [0050]     Output signal  91  is coupled to lens element  82  to provide focusing of the ions for extraction and transport from the ionization region. A feedback device  81  may include a voltmeter for sensing voltages associated with the output signal, such as voltages actually present on lens element  82 . Feedback device  81  generates a feedback signal  83  which may be indicative of any voltage associated with the output signal applied to lens element  82 .  
         [0051]     Feedback signal  83  is received by the input of amplifier buffer  92 , which produces lens element monitor signal  93 . Feedback signal  83  may be scaled, if required, by scaling device  98  and may also be provided to an input of buffer amplifier  88 , as shown in  FIG. 4 , or to lens element bias  90  in order to adjust and increase the precision and stability of output signal  91 .  
         [0052]     Advantageously, DSP  56  may also receive a digital representation of monitor signal  93  provided by ADC  94 . DSP  56  may include hardware and/or software algorithms for monitoring, analysis, and adjustment of signals and for predicting future performance. Monitor signal  93  may be monitored, analyzed, and/or stored in order to improve the precision and stability of output signal  91  and to evaluate instantaneous and trend performance. DSP  56  may thereby predict parameters such as future performance and stability of lens element circuit  80  and lens element  82 .  
         [0053]     For example, DSP  56  may include software enabling DSP  56  to monitor, for example via output signal  91 , a voltage level corresponding with lens elements  82 . DSP  56  may adjust output signal  91  to achieve a desired voltage level. If the required adjustment of output signal  91  changes over time, DSP  56  may store the change. A correlation between the stored change over time versus the physical structure or some other parameter of lens elements  82  may be determined and stored by DSP  56  each time a change in output signal  91  is required, and the correlation and related information may be indicated to the user of mass spectrometer  20 . For example, calibration of lens elements  82  may be completed using a calibration compound of known concentration which results in data of a known peak amplitude. If the calibration peak amplitude decreases, or if the monitored voltage is outside a predefined acceptable range, the condition may be indicated to the user.  
         [0054]     Referring to  FIG. 5 , while the ions are transported from the ionization region and while the ions are trapped in the analysis region, electrode output signal  25  which drives the ring electrode of ion trap electrodes  26  must also be precise and stable. Electrode output signal  25  is an amplitude modulated RF signal on the order of a peak amplitude of 3 kV, for example, and must be precise and stable in phase, amplitude, and frequency. Therefore, production, monitoring, and adjustment of output signal  25  is desirable to reduce drift associated with temperature instability, to monitor the power and efficiency of electrode circuit  22 , to determine the upper mass range available in mass spectrometer  20 , and to more precisely control output signal  25 .  
         [0055]     Referring still to  FIG. 5 , electrode RF circuit  22  generally includes a signal generation portion, power amplifier  28 , power transformer  24 , and circuit feedback. Transformer  24  is essentially a power supply for the ion trap electrodes  26  and provides a step-up primary-to-secondary winding ratio of approximately 100:1 in order to provide a peak amplitude of approximately 3 kV to ion trap electrodes  26 . Maximum efficiency of transformer  24  is achieved by operating transformer  24  in resonance; therefore, monitoring and control of output signal  25  is critical, as lack of resonance will severely impact the gain and therefore efficiency of transformer  24  and electrode circuit  22  in general.  
         [0056]     DSP  56  may specify and generate a digital representation of a desired signal. In the embodiment of circuit  22  shown in  FIG. 5 , waveform memory  34  is coupled between DSP  56  and DAC  32 . DSP  56  may require the use of waveform memory  34  in order to accommodate bus speed limitations of DSP  56  and the high RF frequency of the signal output by DAC  32 . Impedance amplifier buffer  36  is coupled to the output of DAC  32  and provides desired RF electrode signal  37 . Desired signal  37  is provided to an input of power gain amplifier  28 . The output of power gain amplifier  28  drives the primary coil of transformer  24 . Advantageously, transformer  24  may be toroidally-shaped, i.e., doughnut-shaped, transformer such as that disclosed by U.S. Patent Application Ser. No. 60/500,398, entitled “Portable Mass Spectrometer Having Radio Frequency Amplifier Circuitry of Reduced Size,” filed on Sep. 5, 2003, by Knecht et al., the assignee of which is the assignee of the present application, the disclosure of which is hereby incorporated by reference herein.  
         [0057]     In order to monitor the extremely high voltage of output signal  25 , a voltage dividing network including, for example, series resistor R 1  and sense resistor R 2 , may be provided. Sense resistor R 2  has a resistance value much smaller than that of series resistor R 1  so that amplifier buffer  38 , the input of which is coupled to the node between resistors R 1  and R 2 , receives a more manageable voltage which is proportional to the voltage of output signal  25 . Alternatively, the voltage dividing network may be capacitive, or another voltage scaling device known in the art may be utilized.  
         [0058]     The output of amplifier buffer  38  provides RF electrode monitor signal  39 . Monitor signal  39 , or a scaled version thereof provided by scaling device  44 , may be coupled to an input of comparator  42  which also receives desired signal  37  and produces RF electrode error signal  43  as a difference between the two input signals. In order to increase the precision and stability of output signal  25 , error signal  43  may be coupled to an input of power gain amplifier  28 .  
         [0059]     Advantageously, DSP  56  may also receive one or both of error signal  43  and a digital representation of monitor signal  39  which is provided by ADC  40 . DSP  56  may include hardware and/or software algorithms for monitoring, analysis, and adjustment of signals and for predicting future performance. One or both of error signal  43  and monitor signal  39  may be monitored, analyzed, and stored in order to adjust desired signal  37  and improve the performance and stability of output signal  25 , for example, by adjusting desired signal  37  so that transformer  24  is efficiently operating in resonance. Additionally, one or both of error signal  43  and monitor signal  39  may be monitored, analyzed, and stored by DSP  56  in order to evaluate instantaneous and trend performance and thereby predict future performance of circuit  22  and electrodes  26 . For example, DSP  56  may determine component life of electrodes  26 , the mass range of mass spectrometer  20 , or other performance, degradation, or impending component failure. Incidentally, the component life of electrodes  26  may be the time period before the electrodes need to be cleaned. After cleaning, the electrodes may be returned to service.  
         [0060]     DSP  56  may include software enabling DSP  56  to monitor, for example via output signal  39 , a level corresponding with the amplitude modulated voltage applied to electrodes  26  versus a desired amplitude and to adjust output signal  25  to achieve the desired amplitude. If the required adjustment of output signal  25  changes over time, for example, over a period of one hour, DSP  56  may store the change. A correlation between the stored changes over time versus a temperature of circuit  22 , for example the temperature of amplifier  28  or some other environmental condition in circuit  22 , may be determined and stored by DSP  56  each time a change in output signal  25  is required, and the correlation and related information, for example the available mass range of mass spectrometer  20  or a possible temperature failure of amplifier  28  based on the relationship between the amplitude of output signal  25  and the temperature of amplifier  28 , may be indicated to the user of mass spectrometer  20 . Additionally, if the monitored amplitude is outside a predetermined range, the occurrence may be indicated to the user.  
         [0061]     After analysis, ions are detected using one of a variety of types of detectors known in the art, for example, electron multiplier detector  112  shown in  FIG. 6 , and may be preceded after ejection by a conversion dynode. Electron multiplier detector  112  converts the low ion current of multiplier output signal  121  into a higher current using an electron cascading event. For example, electron multiplier detector  112  may be of high impedance providing current gain on the order of six orders of magnitude. The gain of electron multiplier detector  112  is related to the applied voltage of output signal  121  relative to a current detection electrode (not shown). Therefore, a small variance in output signal  121 , which is applied to the entrance or input of electron multiplier detector  112 , results in a very high gain and hence a change in response or baseline noise.  
         [0062]     High frequency noise may result in a spurious signal that appears as though it were related to the presence of a chemical, whereas low frequency noise may appear as though it were a change in baseline noise or a change in the static gain of the detector. Therefore, electron multiplier circuit  110  includes filter network  120  for reducing noise present in output signal  121  and also includes circuitry for monitoring and control of output signal  121 . Electron multiplier detector  112  also decreases in gain as the multiplier ages, thus requiring adjustment of output signal  121  in order to provide the same gain. Therefore, by monitoring the adjustment in the applied potential of output signal  121  to electron multiplier detector  112 , the remaining lifetime of electron multiplier detector  112  may be predicted.  
         [0063]     Digital signal processor  56  may provide a digital representation of a desired signal to DAC  116 . The output of DAC  116  produces desired electron multiplier signal  117  which is coupled to an input of DC-to-DC converter  118 . DC-to-DC converter  118  may be, for example, a step-up converter that provides DC amplification. The output of DC-to-DC converter  118  is provided to the input of filter network  120 , which may be, for example, an RC filter to reduce noise of the provided output signal  121 . Output signal  121  may be, for example, on the order of approximately −1 to −3 kV. Output signal  121  may be turned on and off during the time of one analytical scan.  
         [0064]     A feedback device  131  may include a voltmeter for sensing voltages associated with the output signal, such as voltages applied to detector  112 . Feedback device  131  generates a feedback signal  133  which may be indicative of any voltage associated with the output signal applied to electron multiplier detector  112 .  
         [0065]     Feedback signal  133  is received by the input of amplifier buffer  122  which receives feedback signal  133  and provides electron multiplier monitor signal  123 . Monitor signal  123 , or a scaled version thereof provided by scaling device  128 , may be provided to an input of DC comparator  126 . DC comparator  126 , which may be included in circuit  110 , compares monitor signal  123  with desired signal  117  and outputs electron multiplier error signal  127 . Error signal  127  may be provided to an input to DC-to-DC converter  118 , thereby adjusting output signal  121  in order to provide greater precision and stability.  
         [0066]     Advantageously, one or both of error signal  127  and a digital representation of monitor signal  123  provided by ADC  124  may be received by DSP  56 . DSP  56  may include hardware and/or software algorithms for monitoring, analysis, and adjustment of signals and for predicting future performance. One or both of error signal  127  and monitor signal  123  may be monitored, analyzed, and stored by DSP  56  in order to adjust desired signal  117 , thereby increasing the performance and stability of output signal  121 . Additionally, DSP  56  may monitor, analyze, and store one or both of error signal  127  and monitor signal  123  in order to evaluate instantaneous and trend performance and thereby predict parameters such as future performance, degradation, lifetime, and/or impending failure of electron multiplier detector  112 , output signal  121 , and circuit  110 .  
         [0067]     For example, DSP  56  may include software enabling DSP  56  to monitor, for example via output signal  121 , a DC voltage level applied to electron multiplier detector  112  and to adjust output signal  121  to achieve a desired voltage level applied to electron multiplier detector  112 . If the required adjustment of output signal  121  changes over time, DSP  56  may store the changes. A correlation between the stored changes over time versus an average baseline DC level for mass spectrometry data acquired (which is associated with the available gain of electron multiplier detector  112 , which may decline over time) or some other parameter of electron multiplier detector  112  may be determined and stored by DSP  56 . The stored decline over time may be associated with the lifetime of electron multiplier detector  112 . If the average baseline DC level decreases outside a specified range, then DSP  114  may adjust the DC voltage level for output signal  121  accordingly. Each time a change in output signal  121  is required the correlation and related information may be indicated to the user of mass spectrometer  20 . Additionally, if the monitored DC voltage level has a magnitude greater than approximately −3 kV, or if output signal  121  can not be adjusted to a predetermined range the failure of electron multiplier detector  112  may be indicated to the user.  
         [0068]     The output of detector  112 , i.e., spectrometer data, may be received by the input of amplifier buffer  135 . Advantageously, DSP  56  may receive a digital representation of the output of buffer  135  as provided by ADC  137 . DSP  56  may include hardware and/or software algorithms for analyzing the digital spectrometer data from ADC  137 . DSP  56  may then adjust hardware or signals within any of circuits  50 ,  80 ,  22  and  110  based upon the analysis of the digital spectrometer data.  
         [0069]     Referring to  FIG. 7 , method  150  illustrates the steps of an exemplary calibration of any one of circuits  22 ,  50 ,  80 , and  110  of mass spectrometer  20 . For purposes of illustration, method  150  will be discussed relative to calibration of RF electrode circuit  22 ; however, method  150  may also be associated with circuits  50 ,  80 , and  110 .  
         [0070]     In step  152 , DSP  56 , or another processor or control element of circuit  22 , turns off the output of amplifiers  28 ,  36  and  38 . In step  154 , digital signal processor  56  measures and stores in data block  156  the noise received from ADC  40 . In step  158 , DSP  56  turns on the outputs of amplifiers  28 ,  36  and  38 . Alternatively, the output of amplifier  38  may be turned on shortly after the outputs of amplifiers  28  and  36  have been turned on. In step  160 , DSP  56  measures and stores to data block  162  the noise produced by amplifiers  28 ,  36 , and  38 . In step  164 , DSP  56  generates a low level signal. In step  166 , DSP  56  measures the sample signal and stores in data blocks  168  a signal calibration that is a function of the generated and measured signals, including the noise stored in data blocks  156  and  162 . In step  170 , digital signal processor  56  increases the sample signal level and repeats step  166  as required until a full signal range for DSP  56  has been measured and calibrated.  
         [0071]     Referring to  FIG. 8 , method  200  provides an illustration of exemplary steps for operating any of circuits  22 ,  50 ,  80 , and  110 . In order to further illustrate method  200 , the steps of method  200  will be discussed relative to ion trap electrode circuit  22 ; however, method  200  may be applied similarly to circuits  50 ,  80 , and  110 .  
         [0072]     In step  202 , DSP  56  calculates a desired signal waveform which has been specified by a user or otherwise provided. In step  204 , DSP  56  applies signal calibration factors, such as those stored in data blocks  168  of method  150 . In step  206 , DSP  56  generates waveform data for the desired signal. In step  208 , power gain amplifier  28  and/or other elements of the signal generation circuit, for example, DAC  32 , are turned on by DSP  56 , or another processor or control element. In step  210 , DSP  56  measures at least one of output signal  25 , monitor signal  39 , and error signal  43 . In step  212 , DSP  56  adjusts signal calibration data stored in data blocks  168  based on the measurements of step  210 . In step  214 , if the desired signal is complete, method  200  continues at step  202 , else power gain amplifier  28  and/or other elements of the signal generation circuit are turned off, for example, DAC  32 .  
         [0073]     Referring to  FIG. 9 , a second exemplary method  250  for operating and controlling any of circuits  22 ,  50 ,  80 , and  110  is illustrated. For purposes of further illustrating method  250 , the steps of method  250  will be discussed relative to RF electrode circuit  22 ; however, method  250  may be similarly applied to circuits  50 ,  80 , and  110 .  
         [0074]     In step  252 , a desired signal is specified or otherwise associated with DSP  56 . For example, a user may specify the desired signal, or select a desired signal based on a pre-established configuration or other set-up. In step  254 , power gain amplifier  28  and transformer  24  at least one of amplifies and biases desired signal  37 , providing output signal  25 . In step  256 , DSP  56  monitors and stores in data blocks  257  output signal  25 , for example, by receiving at least one of monitor signal  39  and error signal  43 . In step  258 , if included with circuit  22 , comparator  42  compares monitor signal  39  to desired signal  37  to produce error signal  43 . Error signal  43  is received by power gain amplifier  28 , in order to adjust desired signal  37  and increase the precision of output signal  25 . Alternatively, if comparator  42  is not included in circuit  22 , DSP  56  may adjust desired signal  37  based upon monitor signal  39 . In step  260 , DSP  56  predicts output  25  and other circuit performance, such as the efficiency of ring electrode  26 , degradation, lifetime, impending failure, or other aspects of ion trap  26  and circuit  22 , for example, as discussed above for circuits  50 ,  80 ,  22  and  110 . Specifically, DSP  56  may predict such aspects by analysis of output signal history stored in data blocks  257 . Based on predicted aspects of ring electrode  26  and circuit  22 , in step  262  DSP  56  adaptively adjusts desired signal  37  to increase precision and stability of output signal  25 , for example, as discussed above for circuits  50 ,  80 ,  22  and  110 . Alternatively, or additionally, an indication may be provided that a parameter is outside of a predetermined acceptable range. After step  262 , method  250  continues at step  254  as long as specified desired signal  252  continues. Thus, steps  252  through  262  may be repeated continually and/or continuously.  
         [0075]     Circuits  50 ,  80 ,  22  and  110  have been described above as including a common DSP  56 . However, it is to be understood that each of circuits  50 ,  80 ,  22  and  110  may have its own dedicated DSP. Moreover, it is possible within the scope of the present invention for DSP  56  to be replaced with a different type of processor.  
         [0076]     While this invention has been described as having exemplary embodiments, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.