Lost sensitivity on your Triple Quad or QTRAP You may need to optimize your CEM detector parameter.

Issue Description 

Over a period of several months, you may notice a decrease in sensitivity when using the same acquisition method. One cause can be that the detector voltage (CEM) requires adjustment. The detector in a mass spectrometer will degrade over time, and the detector voltage will need to be increased on a routine basis.

Resolution 

You should optimize the value set for the detector parameter (CEM) regularly to make sure that you are getting the best performance from your instrument. Contact Service regarding the frequency for your system.

The optimization procedure is quick and easy to do yourself. It is performed using the PPG tuning solution in positive ion mode (refer to Table 1 for the appropriate tuning solution to use).

Table 1: PPG Tuning Solution

Note: for TOF instruments, the detector parameter can be automatically optimized using the Instrument Optimization wizard.

Section 1: Analyst® Software and Hardware Setup

1. Open the Analyst software, and select the API Instrument project.

IMPORTANT: The API Instrument project contains all the necessary PPG methods used to optimize the detector parameter for the instrument.  These methods should not be changed.  It is highly recommended to maintain a backup of the API Instrument project.

2. Double click Hardware Configuration under the Configure section of the Navigation bar at the left of the screen.
3. Check to see that the Mass Spec Only profile is active (green check).  If it is not active, select it and then click the Activate Profile.
4. Once the profile has been activated (green check), click the Close button.
5. Double click on Manual Tuning under the Tune and Calibrate section.
6. Fill a syringe with the appropriate PPG tuning solution (refer to Table 1). Use a 1ml syringe with an internal diameter of 4.61 mm.
7. Start the syringe pump at a flow rate of 7µL/min.
8. Set the vertical and horizontal probe settings to 5.

Section 2: Detector (CEM) Parameter Optimization

1. In Analyst, go to the File menu and select Open.
2. Select the Q1PosPPG.dam file from the list and click OK. (If using a 6500 instrument, select the LM method if indicated).  When you are asked if you would like to save the current tuning method, select No.
3. The Q1PosPPG acquisition method will now open in the Tune view.

4. Change Scan Type to Q1 Multiple Ions.
5. Type Q1 Mass of 906.6 and Time of 100 ms.
6. Change Duration to 10 minutes.
7. Click Start, and wait until a stable TIC has been achieved.
8. Click Stop to stop the acquisition.
9. Click on the Detector tab.
10. Lower the CEM value as appropriate:
    • Lower by 100 V for all 2000, QTrap, 3200, 4500, 5500, and 6500 systems
    • Lower by 200 V for all 3000, 4000 and 5000 systems
11. Click Start, and say Yes when asked if you want to save changes made to the instrument data file.
12. Record the Intensity value for the TIC.
13. Increase CEM by the Detector Increment value listed in Table 2.

Table 2: Instrument Detector Increments and Recommended % Intensity Increases

14. Record the TIC Intensity again. 
15. Calculate the percentage increase in intensity using the following calculation:

% Intensity Increase  =   ((2nd Intensity-1st Intensity) / 1st Intensity )    x   100

16. Keep increasing the CEM value by the recommended increment until the calculated % intensity increase is within the guidelines shown in Table 2.
17. Once you have determined the optimum CEM value for your instrument, enter this value into the Detector tab on the method page.
18. Click Stop to stop acquisition. This will save the new optimized CEM value into the instrument data file, and it will then be applied to all existing methods.
19. Close the Manual Tuning mode.  The optimization is now complete.

For other possible causes of low sensitivity on your instrument, visit SCIEXUniversity and view this eLearning module:
SCIEX Triple Quad™ and QTRAP® Instrument Maintenance and Troubleshooting Guide.