With ACQUITY UPLC system, retention time %RSD is inconsistent and increases over time - WKB6687

SYMPTOMS

• Retention time %RSD is not consistent; method does not pass system suitability requirements
  • Increasing retention time shift of 0.4 to 0.5 min from injection to injection
  • Retention trends upward: 2.5, 2.7, 2.8, 3.2, 4.0 min
  • Peak broadening observed
• System pressure increases over subsequent injections, from 6700 to 6850 psi; Delta pressure is stable
• Conducted PM on all system components; shift improved greatly, but still out of specification
  • Retention time trends upward: 2.05, 2.05, 2.08, 2.12, 2.15 min
  • Peak broadening observed
• Column replacement and chemistry (new standards)
• System qualification test results acceptable; baseline to system performance confirmation was made

ENVIRONMENT

• ACQUITY UPLC BSM
• ACQUITY UPLC SM
• ACQUITY UPLC HTCH
• ACQUITY PDA

CAUSE

The gradient method had a higher percentage of organic for the final step (ending conditions), leaving the column poorly conditioned between injections.

The column was not returning to original system pressure at the start of the next injection.

FIX or WORKAROUND

Modifiy the method with respect to gradient conditions:

• Change start and end gradient conditions from original 87%A water to 90%A water.
• Lengthen the last gradient step to ensure that the column equilibrates back to original system pressure at initial conditions.

ADDITIONAL INFORMATION