Dead-stop determination of EDTA and NTA in commercially available detergents

Abstract

A rapid and selective method for the determination of ethylenediaminetetraacetic acid (EDTA) and/or nitrilotriacetic acid (NTA) in commercially available detergents has been developed. It is based on a titration with a standard solution of copper(II) in acetate buffer, where the end-point is revealed by means of a “dead-stop” system with two polarised copper electrodes. Furthermore, it is possible to determine in the course of the same titration the relative amounts of both chelating agents by using 4-(2-pyridylazo)-resorcinol (PAR), which changes colour at the end-point of the first reaction (copper-EDTA). Most detergent constituents, including polyphosphates, have been observed to have no effect on the determination; interference from some constituents (perborates and zeolites) can easily be removed. The method has been shown to give good results in the analyses of different commercially available products.