2695 Separations Module: What to do if negative peaks are detected irregularly - WKB192141

SYMPTOMS

• During a 20-minute run, negative peak appears irregularly, about twice

ENVIRONMENT

• 2695 Separations Module

• 2489 UV/Vis Detector

• A-line: premixed, mobile phase is a water/acetonitrile/TFA mixture

• Flow rate: 0.5 mL/min

• Pressure: ~2700 psi; Δpsi: ~20

• No negative peak observed with Stop Flow

CAUSE

Needle wash solvent contamination/air bubbles/TFA deterioration

FIX or WORKAROUND

1. 0-µL injection, prep injection
   → Determine if the negative peak is caused by the injector motion.
   0-µL injection: negative peak detected
   Immediate injection: no negative peak detected
   For the above result, there is a possibility of a malfunction around the injector and valve. Therefore, after changing the needle wash solvent to the same one as the mobile phase, perform prime and 0-µL injection (also, simultaneously acquire the system pressure data).
   *This is a verification in order to confirm the possibility of needle wash solvent contamination.
2. Obtain system pressure
   → Check for possible affects from bubbles.
3. Prepare and run with a mobile phase without TFA.
   → When preparing the mobile phase, make sure to use TFA immediately after opening the ampoule.
   To assess the possibility of degradation of TFA in mobile phase.

ADDITIONAL INFORMATION