Soil organic carbon determination has two options for indicator
1. Phenolphthalein
2. Ferroin
Is there any difference in result with the use of these indicators in same samples ?
Of course there is difference in results because every indicator works in particular way and according specified mechanisms, some times we kin find difference in same indicator at different times and conditions, so its expected to find difference in results..
The wet oxidation method of soil organic carbon determination is based on a redox reaction. For this reaction, therefore, the Ferroin indicator is used to pinpoint the reaction completion as the redox potential of ferroin indicator is near to the redox potential generated during the redox reaction between K2Cr2O7 and H2SO4. However, diphenylamine is also used as an indicator in place of Ferroin where the use of H3PO4 is a must to bring the redox potential of the indicator near to the reaction redox potential. As, for phenolphthalein, it is an acid-base indicator that changes color along with the change in pH. So, it has to be checked that whether the use of phenolphthalein really gives the correct result in soil organic carbon analysis.
I have used both the indicators for analysis of soil microbial biomass carbon in Inceptisols soils and didnt found much difference in results.
Ferroin indicator may be prefered over phenolphthalein as explained by Dr.Sudeshna.Phenolphthalein turns pink when pH is 8.2 or more.Some workers recommend Ferroin(Ortho-phenanthroline ferrous sulphate (0.025M) over the commonly used diphenylamine indicator.Can some one give the reference for use of phenolphthalein indicator in organic carbon estimation?
Ferroin indicator conserded from redox indicators are fit to this titrations type, but the phenolphathlin indicator as from acid-base titrations , therefore this indicator does not fit for these type of titrations
- Badges
- Science topic
- Similar topics
- Agriculture