To get the Na, Ca and Mg content of soil, I prepared 1:5 (soil:water) extract.
The reading obtained (measured using AAS) are in ppm/l. How do I get (mg/g) concentration value from (ppm/l) units?. and also how to get meq/l value from ppm/l? Do i need to consider the weight of soil and the final volume of extract taken?
Dear Niramaya Muchate.
Reading your question, I guess you weighted the soil.
In that case, is necessary to take in count both soil wieght (mass unit) and final volumen of the extraction (necessary to adjust your result obtained on the aliquote).
Then you can transform your result in ppm to meq using molar mass of each cation and their valence number (n).
Greetings from Costa Rica.
mg/l can be easily converted to mg/g by dividing the value with 1000
Dear Muchate,
By 1:5 (soil:water) extract it seems 1 part soil was extracted with 5 parts solution (10 gram soil extracted with 50 ml solution for example). When it is measured as say ‘x’ ppm (not ppm/l) this means ‘x’ mg of the substance per 1000 ml of extract. Since this extract was obtained by adding 5 times solution it would be 5x ppm in the original soil.
Now ‘5x’ ppm means 5x mg substance per 1000 gram soil. This can be converted to desired units, e.g. (5x/1000) mg/g soil.
To convert into me (which is equivalent weight of an element/group expressed in mg), divide mass of element/substance in mg by the equivalent weight of the element/substance.
Thus 5x ppm of Na (5x mg Na/kg soil) would be (5x/23) me/kg soil or (5x/230) me/100 g soil.
Similarly, for Ca (5x/20) me/kg soil or (5x/200) me/100 g, and
For Mg, (5x/12) me/kg soil or (5x/120) me/100 g
Hello there.
I totally agree with Dr. Borah's answer. Very complete answer.
I would consider also a dilution factor. It isn't usuall to measure directly the extract solution on the analizer.
Firstly the extractant solution must be filtered, and then take an aliquot from the extract solution (in that case, the solution is 50 ml with 10 g of soil filtered) and dilute to a known volume to read on.
In Costa Rica we use cmol(+). kg-1 units (equal to me kg-1).
Greetings from Costa Rica.
Dear Niramaya,
You have prepared 1:5 (soil:water) extract and analyzed by AAS. You are getting conc. of mineral in ppm (mg/L) from regression equation of respective Std. Ok! Calculate the mass of mineral in final volume of extract that's gives you a mass of respective mineral in the original amount of soil taken for extraction. Convert it to ug/gm of soil or whatever conversion you want.That's solved.
Good Luck!
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