6135 MSD Threshold settings between ChemStation C.1.10 and Openlab CDS 2.6

Hi Chris

This may not be definitive answers. 

• I assume that the threshold value is only used for centroid/condensed data, hence is is disabled in the OpenLab method.
• In Chemstation, the peakwidth setting applies smoothing and is used to calculate the cycle time, based on the number of scans/second needed for such a peakwidth
  • In OpenLab, i think the time filter window just applies the smoothing, so you need to change the Scan/Dwell time to ge the same cycle time

Just a comment, though.  You say this method is quantitative, but you are using scan to collect data.  I would normally say that scan methods don't collect enough data points across a peak to accurately/precisely determine the peak area.

Is there no way this experiment could be done with SIM?  I realise that you're in a GMP environment, so method changes are chellenging!

/Andy

Hi Andy,

Thanks for your answer - this is very helpful indeed!

We have seen the threshold value make a difference in ChemStation when running in full/profile mode, but our experience seems to be that responses go down as the threshold is increased.  Decreasing it doesn't seem to have any negative consequences - I'd expected high frequency noise at low abundance in the spectrum to become much poorer, but it doesn't seem much changed (we are operating above m/z 1500 which probably helps).

We had looked at changing the scan/dwell combination and got comparable results so it's very helpful to have that confirmed!

The method is looking for a range of impurities, and critically also for unknown impurities, so SIM isn't an option annoyingly.  We have tried to overcome it by keeping the m/z range as low as possible (m/z 300) to maximise dwell time, and going to low flow rates to give wide peaks to get the best balance of response and an appropriate number of data points.  The method has validated successfully with impurity standard %RSDs around 7-10%.  Any other suggestions or thoughts are always welcome!!

Chris

Hi Andy,

Thanks for your answer - this is very helpful indeed!

We have seen the threshold value make a difference in ChemStation when running in full/profile mode, but our experience seems to be that responses go down as the threshold is increased.  Decreasing it doesn't seem to have any negative consequences - I'd expected high frequency noise at low abundance in the spectrum to become much poorer, but it doesn't seem much changed (we are operating above m/z 1500 which probably helps).

We had looked at changing the scan/dwell combination and got comparable results so it's very helpful to have that confirmed!

The method is looking for a range of impurities, and critically also for unknown impurities, so SIM isn't an option annoyingly.  We have tried to overcome it by keeping the m/z range as low as possible (m/z 300) to maximise dwell time, and going to low flow rates to give wide peaks to get the best balance of response and an appropriate number of data points.  The method has validated successfully with impurity standard %RSDs around 7-10%.  Any other suggestions or thoughts are always welcome!!

Chris