KB001992: What are the Steps to Perform a Capillary Charging Test? - General LC/MS 

The dielectric capillaries for the LC/MSD occasionally exhibit (electrostatic) charging, which causes a loss of low m/z ion abundance. This procedure describes a simple test to determine whether the LC/MSD capillary is experiencing charging.
1. Select a valid small molecule tune file for Positive mode (ES or APCI) in MSD Tune view.
2. Use the Calibrant pull down in MSD Tune to select either calibrant A (for APCI) or B (for ES).
3. Configure the tune file Acquisition Parameters with the parameters: scan range 50 to 3000 amu, Samples 3, Averages 1.
4. Select Acquire MS Data File from the MSD Tune view and create the file charging.d.
5. Select the radio button Use Time (min) and enter a value of 5.
6. After the data file has been acquired, open charging.d in Data Analysis.
7. Extract the following ions and overlay them in the same scale:
a. 121.05, 622.03, 922.01, 1521.97 and 2121.93 for APCI
b. 118.08, 622.03, 922.01, 1521.97 and 2121.93 for ES
8. Compare the relative drop in ion abundance over 5 minutes:
a. If the 121.05 or 118.08 ion shows a decrease of less than 20% relative to the 2121.93 ion,
no action is required.
b. If the 121.05 or 118.08 ion shows a decrease of 20% or more relative to the 2121.93 ion,
the capillary should be passivated with the NaOH passivation procedure.
Notes:
* Charging affects predominantly the low mass ions (121.05 & 118.08). If all the ions decrease 20% or more relative to their starting values, it is probably NOT due to capillary charging.
* Switching ion polarities and profiling should restore ion abundances briefly if the problem is due to charging.
Cleaning the capillary with wire and cotton will usually NOT resolve capillary charging for long.