Contamination of LC/MS Tune Mix - Diagnosis and Fixes

Answer

This Information Applies To: Agilent LC/MS Systems

Issue

Contamination of the tune mix or the Calibrant Delivery System (CDS) of your LC/MS system can cause Autotune failures and drops in sensitivity due to ion suppression. 

Items Required

• Alconox (p/n 5190-1401), or
• Citranox (p/n 5188-5359)
• Ultrapure LC/MS Grade Water
• Ultrapure LC/MS Grade Acetonitrile

Background

Contamination of the tuning or reference mix used on your LC/MS system can occur in several different ways. Diluted and undiluted mix can degrade over time, or due to extreme temperatures or storage conditions.

Often a large cluster of low molecular weight ions will overpower the tuning mix signal at low m/z, see Figure 1 for an example.

Figure 1. Example of Contaminated vs. Clean Tuning Mixes
Top Panel - Contaminated Tuning Mix showing cluster of low m/z ions; Bottom Panel - Same instrument running Tuning Mix from a different bottle.

The process of diluting Tune Mix can also introduce contaminants from solvents, glassware, or pipette tips. Ensure the use of highest grade solvents and clean labware are used for the dilution process. One commonly seen contaminant is Polyethylene Glycol (PEG), which, can be seen as ions spaced regularly 44 amu apart. Figure 2 shows an example of PEG contamination on a G6546A Q-TOF.

Figure 2. And example of PEG contamination, with ions regularly spaced 44 amu apart

The following article details some more common contaminants found in LC-QQQ analysis and how to remove them for your LC-QQQ system: Troubleshooting LC-QQQ Contamination Issues

Resolution

When experiencing contamination isolated to the tuning mix;

1. Clean out the CDS bottle with pH neutral soap (Alconox or Citranox recommended)
2. Triple rinse the CDS bottle with heated (40-60°C) MillQ water
3. Flush out the CDS lines
   1. Fill the CDS bottle with a 9:1 solution of LC/MS-grade Acetonitrile/Water and connect it to the CDS system
   2. Disconnect the PEEK tubing from the fitting at the top of the nebulizer and place the PEEK tube in a clean waste container.
   3. Turn On the Calibrant via MassHunter Acquisition or OpenLab CDS software
   4. Flush the CDS system for a minimum of 15 mins.
4. Rinse and refill the CDS bottle with fresh tuning mix and flush the CDS system with tuning mix for another 15 mins.

Contamination can also come from unexpected areas, such as nitrile gloves. Here are some general rules to minimize contamination from nitrile gloves:

• When using any gloves, try to avoid contact with solvents or soaps, which may extract slip reagents or other chemicals from the glove.
• Avoid powder-coated gloves if possible. If no other gloves are available, then wash them with clean de-ionized water and/or IPA to remove any solid materials or chemical treatments.
• Avoid touching the tune mix sipper line that sits inside the tune mix bottle. It is a common way to contaminate the tune mix.
• Slip reagents on gloves such as Erucamide (C22H43NO, m/z 338.34) have been found to contaminate LC/MS systems from some brands of nitrile gloves.

If contamination persists, then please contact your local Agilent Service Representative.