Baseline drift and cycling when running gradient on ACQUITY UPLC System with PDA - WKB9652

SYMPTOMS

• Baseline drift and cycling observed when running gradient; shows increasing above baseline, then decreasing below baseline, then back to baseline 
• Baseline prior to PM did not exhibit this issue

  • Check valves, mixer assembly, pump heads, and BSM tubing assemblies, including transducer to vent valve, vent valve to mixer, and BSM outlet

  • Passes pump dynamic leak tests

• Running 1.5-min gradient at 1.00 mL/min

  • 100% A (95:5 water/ACN with 0.1M ammonium acetate) to 100% B (95:5 ACN/water with 0.1M ammonium acetate) in 1.2 minutes

  •  Baseline fluctuation as %B increases

  • Requilibrate to initial conditions between 1.2 to 1.5 minutes in gradient method.

  • Ending system pressure returns to expected pressure at initial conditions; delta stabilizes at ~6 psi

• Multiple column positions show the same result

• Column inlet/outlet fitting connections checked; replaced ferrules at inlet

ENVIRONMENT

• ACQUITY UPLC System.
• ACQUITY UPLC Column Manager.
• ACQUITY UPLC PDA Detector

CAUSE

• Poorly made fitting connections between the column manager and the flow cell
• Fitting connections in low-pressure tubing connections (PEEK ferrules and fittings) have been known to loosen over time and may need to be remade

FIX or WORKAROUND

Replace tubing and fittings at the following locations:

• Column Manager outlet valve center port to detector
• PDA flow cell inlet and outlet connections

ADDITIONAL INFORMATION