Complexometric titrations: new reagents and concepts to overcome old limitations

Abstract

Chelators and end point indicators are the most important parts of complexometric titrations. The most widely used universal chelator ethylenediamine tetraacetic acid (EDTA) and its derivatives can strongly coordinate with different metal ions. Their limited selectivity often requires the use of masking agents, and the multiple pKa values of the chelators necessitate a careful adjustment of pH during the procedure. Real world requirements for pH independent, selective and sensitive chelators and indicators call for a new design of these reagents. New concepts and structures of chelators and indicators have indeed recently emerged. We present here recent developments on chelators and indicators for complexometric titrations. Many of these advances were made possible only recently by moving the titration from a homogeneous to a heterogeneous phase using a new class of chelators and indicators based on highly selective ionophores embedded in ion-selective nanosphere emulsions. In view of achieving titrations in situ by complete instrumental control, thin layer electrochemistry has recently been shown to be an attractive concept that replaces the traditional cumbersome titration protocol with a direct reagent free sensing tool.

Development of ionophore-based nanosphere emulsion incorporating ion-exchanger for complexometric titration of thiocyanate anion

“…For fulfilling the conditions of Schwarzenbach, very small size of nanospherical particles, <100 nm [8], [9], [12], ensures rapid phase transfer and so achieve the first requirement. The stoichiometry is well-known from the potentiometric study [6], which achieve the second requirement.…”

Effect of Contamination on the Friction and Wear of Carboxylic Acids in Aqueous Lubricants

“…Under these alkaline conditions, the deprotonation of the four carboxylic acid groups of the EDTA molecule occurs, thus causing the EDTA to have four extra unpaired electrons. As shown in Figure 9, EDTA exhibits multiple coordination groups, and therefore can form 1:1 metal-chelator complexes [29]. As mentioned above, in the lubricating condition where seawater is added to the lubricant containing carboxylic acids, the most probable reactions are between carboxylic acids and Mg 2+ or Ca 2+ bivalent ions.…”

Synthesis of polymer-surfactants by gamma irradiation for removal nickel ions from aqueous solution

“…The residual nickel concentration was determined by complexometric titration with EDTA. The amount of metal ion uptake was calculated from the difference between a blank experiment without polymer and the reading in the actual experiment [30].…”