Date: | 07/03/2023 |
Categories: | SCIEX OS software , Analyst software |
For research use only. Not for use in diagnostic procedures.
Answer
Step 1: Make a first acquisition in MRM with a default cycle time (e.g. cycle time = 0.5 s)
Step 2: Determine the average width of the smallest chromatographic peak (for example 15 s at the base of the chromatographic peak)
Step 3: Calculate the cycle time with the following formula respecting the desired number of points per peak:
Cycle time = Peak width / Number of points per peak (e.g. cycle time = 15/10 = 1.5 s for 10 points/peak)
Step 4-a classical MRM: Determine the dwell time to be applied for each of the transitions in order to obtain the previously calculated cycle time (e.g. cycle time = 1.5 s).
For a fixed dwell time for each transition:
Cycle time = number of transitions x (Dwell time + Pause time between two MRM transitions)
Specifications for minimum dwell and pause times depend on the MS. Per default, the pause time is always set to 5 ms. (e.g. Dwell time = (1500/100)-5 = 10 ms for cycle time = 1.5s, pause time = 5ms and number of transition = 100)
For a variable dwell time:
Use the reference dwell time obtained with the previous calculation and increase/decrease the dwell time for the desired transitions. This decrease will have an impact on the other transitions because the cycle time for variable dwell times is calculated with the formula below:
Cycle time = Number of transition x Pause time between two MRM transitions + ∑ Dwell time for each transition
The following rule must be applied :
If the dwell time of "Y" MRM transitions is increased by "Z" ms then Dwell time of other transitions = reference dwell time - (Y x Z) / (Number of transition - Y)
Step 4-b in scheduled MRM: In sMRM the dwell time for each transition will vary according to the retention time because the number of transitions monitored at a given retention time will determine the dwell time. Analyst or SCIEX OS automatically calculates the correct dwell time for each MRM transition. It will take the largest dwell time value for each MRM transition that allows the desired cycle time determined in step 3 to be respected. Indeed, the higher the dwell time, the higher the signal to noise ratio.
The size of the time windows is an important factor to consider for sMRM methods because the higher the number of transitions with the same retention time (RT ± ΔRT), the lower the dwell time used by the software.
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