Fertilizers usually contain Nitrogen, Phosphorous & Potassium (NPK). Nowadays fertilizers are enriched with micronutrients like Cr, Mo, Zn, Cu, Ca, Mg. They are usually added in fertilizers as their EDTA complexes (Ethylene diamine tetraacetate). Along with micronutrients amino acids are also added. So it is required that amino acids, micronutrient elements and EDTA content of the fertilizer are to be evaluated.
Metal-EDTA chelate
In coordination chemistry, EDTA4- is a member of the polyamino carboxylic acid family of ligands. EDTA4- usually binds to a metal cation through its two amines and four carboxylates. Many of the resulting coordination compounds adopt octahedral geometry.
Because of this ligand’s high denticity, it has a high affinity of metal cations :
[Ca(H2O)6]2+ + H4EDTA [Ca(EDTA)]-2 + 6 H2O + 4 H+
Micro-nutrients are present as their EDTA complex. So EDTA content of the fertilizer cannot be analyzed directly by complexometric titration. Hence EDTA as ethylene diamine tetraacetic acid in regenerated by passing through a column containing strong acid type cation exchanger (Amberlite IR 120) when the cations are replaced by H+ ion and EDTA complexes generate ethylene diamine tetra acetic acid in the eluent. The eluent was analyzed with standard zinc acetate solution at pH 6 (excess PO4-3 present in the solution will not interfere at pH 6 or below) using Xylenol Orange as indicator.The recovery study of Ca-EDTA complex was studied and are as such:
| Sample No. | Conc. Of Metal-EDTA complex in the solution added at top of the column (moles/L) | Conc. Of Ethylene dimine tetra acetic acid in the solution after passing through the column (moles/L) | Recovery (%) |
| 1. | 0.05 | 0.0490 | 98.0 |
| 2. | 0.02 | 0.0198 | 99.0 |
| 3. | 0.01 | 0.0099 | 99.0 |
Since the eluent from the cation exchange column contains excess PO4-3 ion, the analysis of the micronutrient cations are done using AAS with Graphite furnace (for Cd, Zn, Pb, Ni, Mn, Cu) increasing the residence time of the elements in hot zone and AAS with Hydride generator (for As).
Primary amino acids could be quantitatively determined by ninhydrin with the formation of carbon dioxide and an aldehyde. Under some conditions, the ammonia appears as such, but, under others, it condenses to a greater or lesser extent with the reagent to form diketohydrindylidene diketohydrindamine (DYDA). The familiar purple colour which is associated with the reaction of amino acids with ninhydrin is attributed to the anion of this compound.
Ruhemann’s Purple
