Is sensitivity lowered for MRM acquisition methods with polarity switching for a SCIEX 5500 system and other instruments?

For research use only. Not for use in diagnostic procedures.

Answer

In theory, it is possible to have a different signal intensity (usually lower) when a multiple reaction monitoring (MRM) acquisition method switches between polarities on an SCIEX Triple Quad™ or QTRAP® 5500 system. The source and detector might not have enough time to adjust to the exact set voltage, and this could affect the signal.

However, in most cases, if there is appropriate settling time added to the MRM method, sensitivity should not change significantly. For example, for a SCIEX 5500 system, a default settling time of 50 ms is adequate in almost 90% of cases. However, in some cases, this should be increased to 75–100 ms to match the sensitivity of the method without polarity switching. Ultimately the best way to evaluate if the proper settling time is used, the user should compare the signal obtained when running the polarity switching method versus that of the single polarity method. 

Please note that excessive settling time could result in longer method cycle times, and this could affect the number of data points across the peak. If number of data points across the peak is less than 8–12 points, the peak area and signal height might adversely be affected.

For other instruments, the default settling time is different. The default settling times for SCIEX Triple Quad™ and QTRAP® 4500 and 6500/6500+ systems are 50 and 15 ms, respectively.