EDTA titrations have wide applications in inorganic analysis due to its strong complexing effect and commercial availability.5 However, due to the polyprotic nature of EDTA, pH affects the forms present in the solution, and auxiliary complexing reagents are used to prevent the precipitation of metal hydroxides and maintain the concentration of free metal ions.
Direct Titration: Involves buffering the metal ion solution to the desired pH and directly titrating with standard EDTA until the endpoint, as indicated by a color change in the solution.35
Back-Titration: Useful when the metal ions block the indicators, react slowly, precipitate, or form inert complexes. An excess of EDTA is added to the metal ion solution, and the excess is then back-titrated with a standard solution of a second metal ion.
Displacement Titration: Used when metal ions do not react adequately with the indicator. The metal ions are first titrated with a less stable excess of another metal-EDTA complex, and the free metal ions are then titrated with a standard EDTA solution.
EDTA (ethylenediaminetetraacetic acid) can be used to quantitatively determine numerous metals, including Cu (copper), Pb (lead), Hg (mercury), Ca (calcium), Mg (magnesium), Zn (zinc), Cd (cadmium), Ni (nickel), Al (aluminum), Co (cobalt), Mn (manganese), Pb (lead), Zn (zinc), Cd (cadmium), Ni (nickel), Al (aluminum) and Cr (chromium).
These titrations are particularly effective when the metal ions in a sample are titrated in an acidic or basic solution with a suitable indicator. The stability of the complexes formed depends on various parameters, including the pH of the solution.
Copper (Cu): Can be titrated at a pH of about 8 using murexide as an indicator.
Bismuth: Bismuth forms a very stable EDTA complex and can be titrated in acidic solutions where other metals do not form stable complexes with EDTA.
Calcium (Ca): Can be titrated directly with EDTA using murexide or calconocarboxylic acid as metal indicators.
Magnesium (Mg): Can also be titrated directly with EDTA.
Zinc (Zn) and cadmium (Cd): These metals can be titrated at a pH of 10 using Erio T as an indicator.
Mercury (Hg): Can be titrated indirectly with EDTA by first forming a tetraiodomercurate complex and then titrating with zinc sulphate solution.
It is important that titrations are carried out under suitable pH conditions to minimize interference from other metals.
Bild: By Smokefoot - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=64883108
ID: 696
