FTN shows poor repeatability - WKB202956

SYMPTOMS

• RSD for area is between 1% and 2% against the usual 0.1%
• Peak area is slightly different between injections

ENVIRONMENT

• ACQUITY UPLC H-Class

• ACQUITY UPLC H-Class Flow Through Needle (FTN)

• ACQUITY UPLC I-Class

• ACQUITY UPLC I-Class Flow Through Needle (FTN)

CAUSE

The screw between the syringe piston and the syringe motor (see picture below) was not fully tightened, leaving a clearance.

FIX or WORKAROUND

Tighten the screw.

ADDITIONAL INFORMATION

RSD was good with air gap activated, because the gap between the screw and the piston was filled by the motor steps done for the air gap.