Biology Forum Ecology How to measure dry mass?

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    • #9632
      l0sthart
      Participant

      How to measure dry mass? is there any equation or so? Hope to get a reply soon. Thanks (:

    • #84070
      canalon
      Participant

      No equation. One simple experimental procedure:
      take sample put in the oven/desiccator until totally dehydrated and weigh. That simple.

    • #84771
      Cristgonz
      Participant

      canalon is right.
      you don’t need an equation.
      just weigh it and then put it into a "furnace" and then weigh it again (you could know your water and dry mass weight).

    • #84791
      MichaelXY
      Participant

      All bets are off if you try this on the moon however 🙂

    • #84808
      canalon
      Participant

      Not really. If you use a balance calibrated to measure the actual weight in the moon gravity field, it will give you the exact same answer. Why wouldn’t it. Just use properly calibrated instruments. That is what Quality control is used for 😉

    • #84832
      MichaelXY
      Participant

      Yes I realize this, my point was that gravity plays a role in weight.

    • #84835
      MrMistery
      Participant

      or simply measure with the same instrument and multiply by six.

    • #84839
      canalon
      Participant
      quote MrMistery:

      or simply measure with the same instrument and multiply by six.

      Calibration can often be just that 😉

    • #84871
      Cristgonz
      Participant

      go to the moon and measure haha.
      Canalon is right again, just a well calibrated instrument and wuala.

    • #105828
      hsoroosh
      Participant

      I need to measure micro algae dry mass. I’m looking for a way measure it indirectly by spectrophotometer (absorbance) simply. is it possible? immediate reply needed! 🙂 I mean if there is a way I can find an equation to figure out algae dry mass by the solution/culture/chlorophyll/etc absorbance in a certain wavelength.

      Thank you 🙂

    • #105829
      canalon
      Participant

      Easy… Or maybe not.
      Find a relaible measure of the density of your culture for your algae. It does not matter what you are using, as long as you can confidently say that there is a relationship between your measured parameter and the cell density of your culture. And check that it works (do dilutions and count).
      Once you have that measure the relationship between your cell density and the dry mass: i.e. measure the dry masss of the samples that you have used in the calibration of the step above. Redo a few times independantly to make sure that it works nicely.

      Congrats you have your conversion parameters. Enjoy.

    • #105832
      hsoroosh
      Participant

      Thank for quick reply 🙂
      So if I understood truly, I can make a chart with different absorbance and their respective dry mass. and there should be a linear correlation between dry mass-abs . what wavelength you recommend me for that? is 680nm ok? would you please any scientific literature which I can refer to in my writing and references?

      Thank you very much

    • #105834
      canalon
      Participant

      Well I am just suggesting a method that could work. There are no reference because I made it on the spot. I am basing that on the fact that absorption is, within certain limit, linearly correlated with growth in bacteria, and that the size of bacteria will be roughly constant during the exponential growth phase. So I guess, but that is an educated guess, that the absorbance would be similarly correlated with dry mass.
      And I suggested that you verify and calibrate that. But I made the assumption that your microalgae would behave similarly as bacteria, and that there is a known optimal wave length that would give a similarly linear relation with growth. So try and see if that works, if so you can either publish that as a stand alone quick letter to the editor/method paper or just put it as an additional result in your paper and claim the technique for yourself.

      Good luck

    • #105838
      hsoroosh
      Participant

      haha! nice point of view. Your theory should logically work. I’ll try but my time is so tight .

      Thank you anyway for your kind support and efforts 🙂

    • #105941
      hsoroosh
      Participant
      quote canalon:

      No equation. One simple experimental procedure:
      take sample put in the oven/desiccator until totally dehydrated and weigh. That simple.

      Thank you very much. I got a very nice linear relation between dry mass and absorbance in 680nm.it’s y = 0.2372x + 0.019 (R² = 0.9928) which Y is dry mass and x is absorbance for Scenedesmus sp.
      This method is very easy, quick and precise.

      Cheers

    • #105948
      canalon
      Participant

      I am happy to have been of help. Good luck for your future experiments.

    • #105950
      oaktree
      Participant

      If you need to measure by acre, you need a 1.94 m2 frame. Clip everything inside that frame, dry it, then weight. From the measurement (most in grams) you multiply it by 50.

      Example: dry weight is 23.3 g. X 50 = 1165 lbs per acre of forage.

    • #105952
      canalon
      Participant
      quote oaktree:

      If you need to measure by acre, you need a 1.94 m2 frame. Clip everything inside that frame, dry it, then weight. From the measurement (most in grams) you multiply it by 50.

      Example: dry weight is 23.3 g. X 50 = 1165 lbs per acre of forage.

      Your number are probably correct, but have you considered reading the thread before posting?

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