2695 Separations Module: The pump flow rate is normal but the retention time varies - WKB124495

SYMPTOMS

• When run with 1 mL/min, the peak usually appears at 6 min, but it gradually elutes faster from 4.5 min to 4 min.
• Draw the liquid with a syringe in front of the column to check the flow rate → No problem
• Tried two columns of the same type, the same trend was seen
• Same trend seen after repreparing the mobile phase
• The pressure(1300psi) is the same as before, Δpsi is stable with ~13.
• When the column, sample, and mobile phase are transferred and measured with another same system, the peak elutes at 6 min without any problem.

ENVIRONMENT

• 2695 Separations Module
• 2489 UV/Vis Detector
• A line is used for premix, isocratic, and mobile phase
• 20% methanol used for B, C, D line

CAUSE

There is a possibility that there is a GPV open on a line other than A, and liquids from other lines are mixed from there.

FIX or WORKAROUND

1. Prime all lines except A in mobile phase before run, if retention time becomes normal, replace the GPV.

ADDITIONAL INFORMATION