Retention time shift for particular analytes - WKB90951

SYMPTOMS

• Retention time shift (up to 20-30 seconds) for particular analytes (mainly primary and secondary amines)
• Dynamic leak test passes for both BSM pumps

ENVIRONMENT

• ACQUITY UPLC
• TQ Detector

CAUSE

LCMS method lacks robustness due to the unstable pH in ACQUITY (BSM and column).
Switching between different LC methods [using mobile phase B containing additives (buffer or formic acid / acetic acid) and the one  not containing additives] causes instability of pH for the method not containing mobile phase additive. The pH of mobile phase for the method without additives fluctuates depending on how well the ACQUITY was primed/flushed after use of method incorporating mobile phase additives.
For instance, residue of formic acid in UPLC causes retention time shift (toward earlier values) for basic analytes in the LC method not using modifiers for mobile phase B.

FIX or WORKAROUND

1. Modify the LC method and stabilize pH by adding mobile phase modifier (formic acid/acetic acid/buffer).

ADDITIONAL INFORMATION