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3.2 MS

  1. Check oil level in Roughing Pump. If the oil is low or badly discolored, add or change the oil.
  2. Be sure Turbo Pump is spinning full speed as indicated by the meter on the front of the MS. Do NOT proceed if the Turbo Pump is not at full speed.
  3. With the Turbo Pump at full speed, check the high vacuum with the Ion Gauge.

    1. Turn Power to the Gauge Controller ON.
    2. Set the Multiplier to the lowest setting, such 3 (10 $^{\textrm{-3}}$ torr) on some units or 4 (10 $^{\textrm{-4}}$) on others.
    3. Turn the Filament on the Gauge Controller ON. You should be able to see the filament in the Gauge Tube glowing.
    4. If the meter needle goes off scale and/or the filament turns off, there is an air leak. This leak should be repaired before continuing. See Section Vacuum Leak Detection and Repair/High Vacuum Leaks.
  4. Insure that the high vacuum pressure is 1.0*10 $^{\textrm{-4}}$ torr or lower. The lower the better. If the instrument is being Cold Started, this may take considerable time; HP recommends a minimum of 3 hours equilibration time before actually using the instrument after a Cold Start.

    Note: It is a good idea to record in your GC/MS Instrument logbook what this daily pressure reading is, so that you have a record of 'normal' operating pressure for your instrument. This can greatly simplify troubleshooting vacuum problems.
  5. Reset the Gauge Controller Multiplier to its lowest setting.
  6. Very slowly, and while watching the Gauge Meter, open the calibration gas valve. You may see the needle rapidly increase then decrease. After this jump, it is okay to open the valve the rest of the way. Make sure the pressure goes back below 1*10 $^{\textrm{-4}}$ torr before proceeding.
  7. Turn OFF the Ion Gauge Filament and Power.
  8. Launch the ChemStation Software (if not already running).
  9. If doing a Cold Start or if you suspect a small leak (the Step 4 reading higher than normal but still in the 10 $^{\textrm{-5}}$ torr range or lower), run the Air/Water Check utility. The m/z 28 and 32 signals should be smaller than m/z 18. The m/z 18 should be smaller than the PFTBA m/z 69.

    If the Air/Water Check does not pass, it could be that the system simply has not pumped long enough after a Cold Start, or there may be a small air leak.
  10. Perform an MS Autotune if needed. HP does not recommend autotuning their instruments daily, unless there is some compelling reason to do so for instruments used continuously or in Stand-By mode when not in use. Autotuning every other day or once per week is generally adequate.

    An Autotune should be always be done after a Cold Start.

    The Autotune printout should be saved in an MS Autotune Logbook for your instrument. The operator should examine the Autotune printout and compare the new Autotune parameters to the last Autotune parameters:

    1. Dramatic changes of any parameter are often an indication of an instrument needing maintenance.
    2. The EM Voltage (usually somewhere around 2000 Volts) will gradually increase as the EM ages.
    3. When the EM voltage gets to around 2500 Volts, it is a good idea to order an EM.
    4. Mass axis calibration should be within about +/- 0.2 amu for the three PFTBA peaks m/z 69, 219 and 502. If the masses of these three peaks deviate by more than 0.2 amu, rerun the Autotune to see if the mass calibration improves.
    5. Signal widths at half height for each of the three tune peaks should be about 0.55 - 0.60 for the default ChemStation Autotune routine. If any of the peak half widths are less than 0.55 or greater than 0.60, rerun the Autotune to see if the widths improve.
    6. The m/z 219 should generally be about 40-60% of the m/z 69 signal. If it is not, rerun the Autotune to see if the signal ratio improves.
    7. The m/z 502 should generally be about 3% (5% is okay, but smaller than about 3% may be an indicator of an instrument that requires maintenance) of the m/z 69 signal. If it is not, rerun the Autotune to see if the signal ratio improves.
  11. If the MS has passed the Autotune, close the calibration valve.

next up previous contents
Next: 4 Putting the GC/MS Up: 3 Warm Start: Starting Previous: 3.1 GC   Contents
John S. Riley, DSB Scientific Consulting