When we are doing heavy metal extractions from plant samples we use acids like HNO3 or HCL .
I want to know what is the importance of these acids in extraction and I need to know about the mechanism of the action of the acids.
Most of the metals by acid extraction... form either M nitrate, M sulfate or M phosphate..... That will detect by ICP analysis... in which different metal nitrates are used for standards..........
Principles of Acid Digestion and Selection of Acid
(i) HNO3 acts as both acid and oxidizing agent
As acid it dissolves inorganic oxides
CaO + 2H3O+ → Ca2+ + 3H2O
As oxidizing agent HNO3 can oxidize zero valence inorganic metals and non-metals into ions
Fe + 3H3O+ + 3HNO3 → Fe3+ + 3NO2 + 6H2O
3Cu + 6H3O+ + 2HNO3 → 2NO + 3Cu2+ + 10 H2O
(ii) HNO3 does not form any insoluble compounds with metals and nonmetals, whereas H2SO4 and HCl do
Zhang, C. (2008) Fundamentals of Sampling and Analysis. Wiley.
Amino acid is highely found in plant, source of growth regulater and many toxic heavy metal found in acidic solution . then we are analysis in HCl extracts and convert in easy oxidizing complex.
Basically, it is not only "heavy metal extraction", but the sample digestion/dissolution problem.
correct me if i'm wrong , as i know the HCl and HNO3 acid used to make the heavy metals "visible" when used on spectrophotometer
I agree with my colleagues. Basically acid is used to release metal from matrix and make available in water for easy and accurate analysis .
Heavy metals present in any of the materials like plants, soils, solid waste can be extracted or leached using strong or weak acid and it also depends upon the solubility of the respective metal. In general, metals are in soluble in acids (HCl, H2SO4, HNO3, etc,). Like for example, Cu can be extracted using acid (say H2SO4) and will form of copper sulphate. However, this will happen only when the pH of the acid solution is less than 5.5. This is true for most of the metals like zinc, nickel, lead, cadmium, iron,etc. In the presence of alkali, metals in solutions tends to precipitate.
Cu + 2OH- -------> Cu(OH)2 (ppt)
Also metals in solution can only be detected or analysed from aqueous solution when the pH of solution is acidic.
acid is used to release the metal available to be determined. Moreover, acidic environment helps detect the metals.
Most heavy metals exist in combination of other organic materials in soil or plant matter, therefore acid help in breaking existing bonds between the metals and the matrix in which they are to be extracted from. Most metals however require acid digestion for solubility purpose.
The acid is used to release the metals from the matrix allowing it to be analysed. For contaminated land work the acid is used to dissolve the soil only leaving the contaminates which will most likely be metals.
Acids are used to digest the sample. For SELECTIVE and EFFICIENT metal extraction one need to perform multiple metal-chelate or ion-pair extraction.
The concept of acid in use to converting in soluble form heavy metals samples.
Dr.Rabbani,You are right. Dr .Olawale reply is also equally right.Elemental analysis of plant sample or compost sample requires destruction of organic matter for bringing the heavy metals in solution form.When organic matter is destroyed,the mineral matter automatically comes in to solution.Acids or their combination also differ in their action on organic materials of diverse nature.Among the acids, the concentrated nitric acid appears to work better.The following paper gives good comparison of methods.
Evaluating heavy metal contents in nine composts using digestion methods. by Zeng-Yei Hseu Bioresource Technology 95(2004)53-59.Available online at www.sciencedirect.com.
I agree with Annagi Subba Rao. Further, please read some basic books on methods for heavy metal analysis. I am sure DU would have such books in bulk.
We have extracted heavy metals using Nitric Acid. A number of acids are efficient in decomposing samples of rock, soils or sediments. Acid mixtures (hydrofluoric-perchloric-nitric or perchloric-nitric) are especially effective in decomposing such samples. Concentrated nitric acid alone has a less vigorous effect than mixed acid decomposition methods and, in particular, Fe (III) oxide minerals are not attacked strongly. However, Nitric Acid is very efficient for the exxtraction of heavy metals such as Cd, Cu, Pb and Zn.
Regarding metal analysis in plant, HNO3 is efficient than others and the mechanism has been clearly explained by D.B.Short. In cases of soil digestion Triple acid mixture could used.
It helps to avoid oxidation of metals as well as reactions and interactions with the container.
Most heavy metals exist in combination with other organic materials in soil or plant. adding acid or digestion of sample with acid helps in breaking the existing bonds between the metals and other compounds in the samples.
Digestion of samples in acid helps to remove impurities/interference, bring the metals into solution as ions and make the sample readable by the analytical instrument (AAS, ICP-OES, ICP-AES etc.).
To break links (bonds) between Metals and organic elements, in order to make them accessible to dosage. We often use Nitric acid (Or a mixture of three acids).
To break the bond of metals and other organic element so as to access a dosage of the metal via AAS
- Badges
- Science method
- Similar topics
- Biological Science
- Ecology