Arc cycling baseline during gradient - WKB69452

SYMPTOMS

• Sinusoidal baseline during gradient
• Magnitude of wave changes depending on path
• Magnitude changes as gradient progresses
• Number of cycles per minute in the baseline is similar to number of cycles of pump strokes per minute
• Delta psi is 15-16 psi, 0.4% of system pressure
  
  
  
  
   

ENVIRONMENT

• ACQUITY Arc
• 2998 Photodiode Array Detector
• ACN
• H₂O

CAUSE

Poor mixing

FIX or WORKAROUND

Change the plunger stroke volume from 132 µL (default) to 66 µL.
With a 66-µL stroke volume: 
- This does not change the dwell volume
- It is useful for long, shallow gradients
- It reduces the baseline noise caused by pump pressure fluctuations 
- The maximum flow rate that the Arc Solvent Manager delivers will be limited to 2.5 mL/min and below

ADDITIONAL INFORMATION

Depending on the method, the path 1 mixer may not exhibit the cycling baseline symptom because it is longer and provides better mixing.