Service Note
Subject:  5972-21 
     
SUPERSEDES:  None
     
HP 5972A Mass Selective Detector
Serial Numbers:  0000A00000 / 9999Z99999 
     
HP G1034C rev. C.03.03/C.02.09/C.01.10 Patch / p/n G1034-10063 
HP G1701AA rev. A.00.01 Patch / p/n G1701-10001
     
Default Filament Emission Current Lowered to 35 uA
     
Situation:  
The 5972A filament emission current setting is hardcoded in the tune 
macros at 50 uA.  This setting was established as the optimum value 
for greatest instrument sensitivity at the time of the 5972A's 
introduction.  Within the past year, however, there has been a change 
in the emission characteristics of the filament.  Since this change, 
an emission current setting of 50 uA no longer produces optimum 
sensitivity for most 5972As.  For these instruments, a lower filament 
emission current can give improved instrument sensitivity and more 
stable ion ratios. 
     
For currently installed 5972As, this problem will most likely occur 
when the filaments are replaced.
     
To determine whether the filament emission current setting is too 
high, inspect the repeller ramps, since the emission current has a 
significant effect on the repeller ramps.  The diagrams below 
illustrate the effect of emission current on repeller ramps:  the 
first one shows a repeller ramp where the emission current is too 
high; the second one shows a typical repeller ramp where the emission 
current has been optimized.
     
Repeller Ramp--Emission Current Too High
     
  |                                                              . + * 
  |      ....  69 m/z                                            . + *
  |      ++++  219 m/z                                                        
  |      ****  502 m/z                                          . +  *
  |                                                            
  |                                                           .  +  * 
  |                                                            
  |                                                         .  +   * 
  |                                                   
  |                                                       .  +    * 
  |                                                     
  |                                                   .    +     * 
  | 
  |                                               .     +       *
  |                                       
  |                                           .      +        * 
  |                                       
  |                                       .      +          * 
  |                                    .       +          *
  |                               .         +           * 
  |. .  .   .    .     .     .        +            *
  |+ +  +   +    +     +      +              * 
  |* *  *   *    *     *       *       
  |___________________________________________________________________ 
  0V                              20V                             40V
     
     
Repeller Ramp--Emission Current Optimized
     
                                 69          219      502
                                  |           |        |
  |                             .  .         +  +    *  *            
  |                           .       .   +       +         *      
  |                         .          .         *                 
  |                        .           +.           +            *   
  |                                           *              
  |                      .           +    .           +              * 
  |                                         *               
  |                     .          +         .         +       
  |                                                        
  |                    .         +       *       .       +    
  |                                                     
  |                   .        +                      .    + 
  |                                   *                   
  |                 .       +                                +.
  |                                *                                 . 
  |               .     +                                      +
  |                             *          
  |            .     +                                            +  
  |                         *                                        +  
  |        .     +      *                          
  |           +    *
  |   .  +   *
  |. + *
  |___________________________________________________________________ 
  0V                              20V                             40V
     
     
In the first diagram, all three masses maximize at or near the maximum 
repeller voltage.  In the second diagram, the three masses maximize in 
a repeller voltage range of 20-35 V.  
     
The problem with the first diagram is that the standard spectra autotune 
tunes with a fixed repeller voltage of 25 V.  At 25 V, the three masses 
in the first diagram are only at 10-25% of their highest abundances in 
the ramp.  This translates into reduced sensitivity.  At 25 V in the 
second diagram, all three masses are at or near their maximum abundances.  
The same effect occurs with a maximum sensitivity autotune.
     
Caution:  A dirty source can give repeller ramps similar to the ones in 
the first diagram.  Make sure that the source has been cleaned before 
attempting to optimize the emission current.
     
     
Solution/Action:  
For new systems, the 5972A will be tested with the filament emission 
current set to 35 uA, and the HP G1034C and G1701AA MS ChemStation 
software will ship with the default 5972A filament emission current set 
to 35 uA.  
     
For 5972A systems already installed, how you change the default filament 
emission current depends on the type of data system which is configured 
with the 5972A.
     
-  For HP G1034C MS ChemStation:  Install the patch p/n G1034-10063,
rev. C.03.03/C.02.09/C.01.10.
     
This patch installs modified ATUNE72.MAC, TTUNE72.MAC and DIAG72.MAC 
files in the C:\HPCHEM\MSEXE directory.  In the new files ,the
MSPARM EMISSION,,50 line has been commented out in the tune macros, so 
that the emission current setting will no longer be hardcoded but 
instead will be taken from the tune file (atune.u, bfb.u, dftpp.u, 
etc.).  The patch also installs new default tune files with an emission 
current setting of 35 uA in the C:\HPCHEM\MSSETUP\5972 directory.
     
-  For HP G1701AA MSD ChemStation:  Install the patch p/n G1701-10001, 
rev. A.00.01.
     
This patch makes the same changes to the software as the patch for the 
HP G1034C software.
     
-  For HP 59944B/C HP-UX ChemSystem:  There isn't a patch.  Contact MS 
Product Support for the modified tune macros.
     
     
Even after installing the patches and/or modifying the macros, the filament 
emission current setting still needs to be optimized and saved in the
tune files (*.u).  This should be done any time a filament is replaced.
     
1. Perform a standard spectra Autotune.
     
2. After the tune has completed, start up Manual Tune and load the 
tune file atune.u.
     
3. Go into Edit MS Parameters.
     
4. Click on the repeller field, then click on Ramp at the bottom of the 
screen.  A repeller ramp should be performed.
     
5. Inspect the repeller ramp and note the repeller voltage where 219 m/z 
is maximum.  For optimum sensitivity and ion ratio stability, the maximum 
219 m/z should be at a repeller voltage of 30 V.  If 219 m/z maximizes at 
a higher repeller voltage (or if the repeller ramp looks like the first 
diagram in the Situation Text above), adjust the emission current to a 
lower value, as follows:
     
6. Click on the Emission field and lower the emission current by 5 uA. 
Click on the repeller field, then click on Ramp at the bottom of the 
screen.  Inspect the resulting repeller ramp and note the voltage at 
which 219 m/z is maximized.  Repeat this step until the maximum 219 m/z 
corresponds to a repeller voltage of 30 V (see the second diagram in
the Situation Text above).  The emission current should be approximately 
in the range 20 - 35 uA.
     
7. Save the atune.u tune file.
     
8. Load any other tune files on the system (bfb.u, dftpp.u, ttune.u, etc.), 
and change the emission current setting in those tune files to the value 
determined in step 6, then save those tune files.
     
     
Date:
27 November 1995
     
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*                     INFORMATION ONLY                        * 
*                     ----------------                        * 
* AUTHOR/ENTITY:_______  SL/2300 ___________________________  * 
* ADDITIONAL INFO:_______None_________________________________* 
*                                                             * 
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