Hi!
I am trying to measure the energy content of various gelatinous zooplankton organisms using a semi-micro bomb-calorimeter. Because of the low expected energy content, I am mixing my sample 1:1 with my standard (i.e. benzoic acid). Both gets pressed into one pellet (about 0.4 g). After the combustion, quite some remains are in the bomb, probably due to the high salt content.
The determined energy value is, however, one order of magnitude lower than published values (0.15 versus 2-4 kJ/g DW).
Does anybody have a suggestion why this is the case and how to improve the routine?
I appreciate any answers.
Best, Florian
Hi Florian
I suggest to dry your sample : slowly, not at too high temperature.
Empty can help.
When drying you have to evaporate only water and not organic compounds.
May be degrading your sample by ultrasound before drying is a way to evaporate water at low temperature.
But you have to weight before and after drying to know the amount of water.
After you can use your calorimeter on this dry (or less wet) sample.
At the end, you take account of water content only by the latent heat of vaporisation of the water in your initial sample.
Best regards
Paul
Hello Paul,
thank you for your fast reply. I should have said that all jelly samples were freeze-dried (vacuum, -45 °C for at least 96 hours) before bomb-calorimetry. This is a standard procedure used regularly in the literature. The energy values is based on dried material only. Do you have another suggestion why the reading was so low?
Best regards, Florian
Hello Florian
I have no better solution.
However, as you suspect your measured value, may be you have unexpected salt content but i suppose you know this.
The only other way to have a low LHV is the presence of oxygen and nitrogen in the organic part but the LHV of protein, or cellulose ... is not so low.
For me it is difficult to eliminate salt and mineral by washing : I did not succeed on algae.
It could be interesting to estimate the salt or other mineral content by pyrolysing your dry sample.
After that may be evaluating C H O N S content can give you a mean to estimate the LHV.
Sorry not to be able to help you more.
Best regards
Paul
Hey Florian, Did you measure organic carbon content in similar samples (i.e. rinsed, freeze dried and weighed)? That would give you a clue whether your samples contain more salt/less tissue than you expect. cheers Leni
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