Low sensitivity on negative ion mode MRM transitions - WKB23945

SYMPTOMS

• Low sensitivity on negative ion mode MRM transitions in a fast switching method
• Positive ion mode transitions OK
• Negative ion mode sensitivity test passes
• If negative ions are acquired in isolation, sensitivity is as expected

ENVIRONMENT

• Xevo TQ-S micro
• Xevo TQ-S
• Xevo TQ-XS

CAUSE

Dirty ion optics and very low dwell times

FIX or WORKAROUND

1. Clean ion optics: ion block, stepwave, segmented quad, MS1 quadrupole, collision cell, MS2 quadrupole.
2. Set interscan and interchannel delays to automatic.

ADDITIONAL INFORMATION

As the ion optics get dirty, voltages on the optics take longer to settle when pos/neg switching. The instrument optics must be very clean to run at very short dwell times (e.g., less than 5 ms).