WHAT IT IS
Polarity switching is when the mass spectrometer rapidly changes between positive and negative ion detection during a run. This allows analysis of compounds that ionize in different polarities without running the sample twice.
HOW IT WORKS
The instrument changes ion optics and detection settings to match the desired polarity. In positive mode it detects cations; in negative mode it detects anions.
Switching can be very fast — modern systems achieve 5–50 ms in triple quads, ~25–30 ms in Orbitraps, and up to ~0.7 s in some high-resolution modes.
IMPACT ON PERFORMANCE
- Covers more analytes in one run
- Saves time by avoiding duplicate injections
- Useful in multi-class methods like pesticides or metabolomics
CHALLENGES AND LIMITATIONS
- Shorter dwell time if too many switches per cycle.
- Sensitivity loss if switching is slow or poorly optimized.
- Not all systems can switch fast enough for very narrow LC peaks.