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

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).

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

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 😉

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

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

Calibration can often be just that 😉

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

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 🙂

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.

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

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

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 🙂

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

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

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?