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

Hi All,

Working in a GMP environment and we need to transfer an LC/MS method from a site using ChemStation C.01.10 to a site using OpenLAB CDS 2.6.  Most of the method settings transfer easily, but we're having some difficulties determining the appropriate threshold settings and making sure that the peak width/cycle time/dwell time are the same.  The method is quantitative so these are quite impactful.

In the original ChemStation method the threshold is set at 50, but it looks like that option isn't available in OpenLAB 2.6?  Does anyone know how Openlab treats the data instead?

We'd also assumed that the time filter window in OpenLab was the same as the combination of the time filter and the peak width in ChemStation, but we seem to be getting a different cycle time (0.479s rather than 1.9s).  Is the scan/dwell time a new option in Openlab and is this what needs to be edited to get the same cycle time?

Finally, I'm assuming that "Profile" data storage in Openlab is equivalent to "Full" data stroage in CS?

Thanks in advance! Chris

  • 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 Chris, any resolution for this? We are noticing an issue of reduced sensitivity for low-lying impurities which might be based on the threshold when collecting Full/Profile using Scan as well. 

  • Hi Brij, I think this ended up being something we just accepted.  A bit of feasibility work across the two systems showed that the data were reasonably comparable with whatever default settings OL CDS uses  for the threshold (ie: there wasn't orders of magnitude difference).  It hasn't caused us many issues.  

    The peak width setting has been replaced by the scan/dwell time so it was straightforwards to do the maths to get equivalent settings for that.

    I suspect this may not be much help for you though I'm afraid!  Are your sensitivity issues due to reduced signal or increased noise?

    Chris

Was this helpful?