Loss of sensitivity over time with UniSpray - WKB30509

SYMPTOMS

• With UniSpray, MS signal decreases with each injection

• When running the same method with ESI, no issue is observed

• When running with standards in MilliQ water, no issue is observed

• Accumulation of white material on the UniSpray impactor

ENVIRONMENT

• Xevo TQ-S (for all compatible MS systems)
• MassLynx 4.1 (for all compatible MS software)
• Waters UniSpray Ionization source

CAUSE

The method includes large injection volumes of water. This contains inorganic salts that upon evaporation of the solvent during the desolvation process deposit on the impactor. The deposit of white material on the impactor may prevent correct ionization of the compounds.

FIX or WORKAROUND

Diverting the flow to waste at the beginning and at the end of the chromatography will prevent the accumulation of this material on the impactor.

ADDITIONAL INFORMATION

For information on diverting flow to waste, see article 12652.