I am performing some DSC (perkin elmer 8500) measurements (same materials, same mass, same program). Following calibration, I encountered different baselines every day. The baseline was flat only on the first day. Any idea what's happening? Does the instrument need to be calibrated every day?
Baseline of instrument effects due to use of DSC cell if you use cell for long time period so base line is effected
baseline of instrument due to decomposition of material on cell
The shift of the baseline is due to a heat flux between the two cells.
A flat baseline is obtained when a perfect symmetry of the two cell (same sample holder, at the same place, etc.) Did you check if your sample made a deposit on the measuring compartment? Do you use an empty cell as the reference ? I don't know the PE 8500, but it is given for 750 °C max. Check if a calibration of the baseline is needed in the instructions. This step may be done using two identical empty cells. You may have to do that every day.
Michael Shuster Yes, I am using aluminium pans, could it be the reason?
Jean-François Gal My samples are metallic alloys with melting temperature around 900 C, and I am doing DSC up to 600 C. Also, I crimp the samples in the aluminium pan (and always checking the bottom of pan to be flat). Yes, I use an empty aluminium pan as reference.
Just a few thoughts. 1. The baseline should be calibrated within the temperature range extended beyond the range of your runs. 2. While 600C is below melting point of your alloys, it is possible that at such high temperature aluminum pans may deform or react with the alloy. 3. May be, you should try performing your baseline calibrations and runs using platinum or ceramic pans.
Note that my experience is limited to mower temperatures and organic compounds. I think the Michael Shuster suggestions are commandable.
Dear Michael Shuster and Jean-François Gal ,
Thank you for your time and advises. The thing is that even with empty pans the baseline is not stable. And, the temperature limit of instrument is 600 C.
I afraid that, if the baseline instability is the instrumental artifact, hardly you can fix it. What do Perkin Elmer guys say?
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