Please, in order to be able to analyze the mineral composition of an aqueous extract of plants in ICP , how can we prepare the samples? what are the steps to do the acid dissolution? choose solid acids (citric acid) or liquid acids (nitric acid)?
There is no one ideal or one universal way to prepare samples for analytical measurements, e.g. elemental composition. It all depends on what you want to know about your samples. So you, as the person conducting the research, should determine what information about your samples you need, and another person, who is a specialist in the field of chemical analysis of biological materials (in this case, plant materials), should determine what could be used for a given purpose and is it feasible and under what conditions. Therefore, if you want a specific hint, you should ask about very specific matters. Your question is too general.
As well as echoing the comments in Zbigniew Jońca 's answer, can you specify if you want to (1) analyse solid plant material that has been digested to break down the solid matter and dissolve the metals, or do you intend to (2) analyse "aqueous extracts" from plants, i.e. sap, root exudates and the like?
Option (1) sounds like typical digestion processes, of which there are dozens of recipes in the literature. These are fairly routine procedures, but require significant equipment, training and practice to yield good results when first starting out. Do you have a local technician at your institution that can assist you?
Option (2) requires a different set of skills (and equipment) to collect small masses or volumes in clean (metal free) conditions and dilute these samples to sufficient volume to introduce to the ICP without losing too much sensitivity for the very low masses of metals you are likely to collect.
Perhaps if you can elaborate on your target elements and samples, we can provide some more specific information.
my sample is an aqueous extract of plants, in which I want to measure nitrogen, potassium, oxygen, phosphorus
Follow the digestion procedures for dried plants of the AOAC (Association of Official Analytical Chemists).
I do not believe it is possible to measure Nitrogen or Oxygen by ICP-OES because of air and water backgrounds.
For the other elements just add some nitric and/or hydrochloric acid to your extracts in the same concentration as in your standard solutions.
Cheers, Ulrich
The mixture of HNO3 and H2O2 looks the preferable for complete plants decomposition.
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