Hi everyone,
I am doing MRM on our Micromass API MS.
I am wondering how should I set the scan times, like inter-channer delay, inter-scan delay and dwell time? any tips for these settings? I am using both negtive and positive for about 40 chemicals.
I am a bit confused by these times?
many thanks.
Are you want to separate the 40 compounds at a single running? The best total scan time is 1 ms, so if I need four channels for monitoring four compounds I usually set 0.25 ms for per channel.
However I didn't monitored so many chemicals at same time. So you maybe set 0.025 ms for your scan time for 40 chemicals. Or you can also increase the total scan time to 2, or 4 ms for a try.
Good Luck.
Wenxue
The inter-channel delay and inter-scan delay can be set as low as possible, this manual should provide information on this, these are the times between each MRM channel. The dwell time is how long each MRM channel is monitored. You will want to experiment with this to give around 10 points per chromatographic peak. You can also set the acquisition to only perform the MRM for a particular compound in a retention time window that corresponds to when that compound elutes from the column, this allows a small number of MRMs to be measured at various times throughout the analysis rather than all 40 MRM for the whole analysis. Doing this means that the dwell time for the MRMs can be increased.
for example if you have 2 compounds the elute at 2 mins (compound X) and 4 mins (compound Y) then you monitor the MRM for the compound X for a window of 1.5 min to 2.5 mins, then change to monitor compound Y for a window 2.5 min to 4.5 min. The dwell time can be set to 1 ms (for example) whereas it would have to be set to 0.5 ms if both MRMs were monitored for 1.5 to 4.5 mins in order to get the same number of sample points per chromatographic peak.
Hello,
On MassLynx method editor you will see and inter-channel delay window time (for your purpose usually at 0.02) and an inter-scan delay window time (set at 0.1). Then based on the retention time of each compound on the method editor you will set the time for scanning interval between the beginning and the end of the peak
See the document attached
Horia
Thanks a lot guys.
if I want to scan both positive and negtive for a specific time period like 10-15min, should I set the inter scan delay time at 0.1s or 0.3s?
To Daniel, do you mean 1s ranther than 1ms in your example? I think the unit for dwell time is s, right?
to Horia, thanks for the document, can I ask which version do you use, 4.1?
seems we have different view of the MRM fuction. I noticed you setted the inter-channel delay and inter-scan delay as 0.02 and 0.1, why do you set as this? can I use lower because I might scan for 5 chemicals (10 channels) for each function?
I set my MRM fuction (see attached file) similar to this paper, and my cycle time is 1.33s,
but I got this peak shape (bad, see attached file), what was wrong with my setting?
how should I set then?
many thanks.
Article Multi-Class Determination of Around 50 Pharmaceuticals, Incl...
The dwell time is how long each MRM is monitored, the cycle time is how long it takes to do all the MRMs and it will be the time between each data point for any particular MRM, this is why you have only a few data points on the peaks in your chromatogram. You need to decrease you cycle time, the only way you can do this is breaking up the numbers of MRMs you are monitoring into different time sections (also see my previous post). In this way you are monitoring a fewer number of MRMs at any time and the cycle time will decrease. The paper you reference uses both this method (see pages 2268-9) and a dwell time of 0.01 secs
The inter-scan delay (ISD) is the time to swap from +ve to -ve and hence needs to be slightly longer than the inter-channel delay (ICD) which is the time between each MRM in the same ionisation mode. I see that your ISD is set to 0.3 secs, the paper uses 0.02 secs.
regards
Daniel
Hi Daneil, I tried setted the scan time as the paper did:
dwell time 0.01s and ISD 0.02s, but I still got bad peak shap. (see attached).
seems too small?
thanks.
chang'er
Your "interscan delay" is still too large, it is set to 0.3 secs, it should be 0.01 secs. You could also consider sorting your MRMs into different retention time windows so that the system is only looking for a compounds MRM when it is eluting. The effect of this is that the instrument is doing less MRMs at any particular time.
There appears to be no compounds eluting between 8 and 9 mins, so the MRMs for compounds that elute between 5 and 8.5 mins could be one function and compounds eluting from 8.5 mins to 12 mins could be a separate MRM function.
Thanks Daneil, for the second gragh, I set the interscan delay as 0.02s.
I use both neg and pos modes, does this affect the interscan delay, someone told me if search for both modes, need set this delay longer, is this correct?
The positive/negative are performed as 2 separate functions, all the positive MRMs then all the negative MRMs, so it only switches from positive to negative once per cycle, 0.02 sec is OK.
Did you get the similar results after changing the interscan delay, the data you posted shows different retention time regions.
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