Sequestering agent chelates

The major mode of polyacrylamide decomposition at elevated temperature (in the absence of oxygen) is hydrolysis (319,320). Thus, the concentration of divalent metal ions has an effect on viscosity retention at high temperature. Chelating and sequestering agents have been used to reduce the adverse effect of... 

Most divalent and trivalent ions, with the exception of the alkaline-earth metals, are effectively chelated by the hydroxycarboxylates citric and tartaric acid, and citric acid will also sequester iron in the presence of ammonia. Another hydroxycarboxylate, gluconic acid, is especially useful in caustic soda solution and as a general-purpose sequestering agent. 

Wool is exceptionally prone to absorb metal ions, particularly in the weathered tips of the fibres, leading to shade differences on subsequent dyeing, especially if chelatable dyes are used. Hence sequestering agents can be essential additions to scouring, rinsing and dyeing... 

A substance which results in the chemical inactivation of a metal. The catalytic effect of heavy metals, mainly copper and manganese, on the oxidation of unsaturated compounds such as rubber, results in very rapid deterioration. Chelating agents convert the metal into a chelate co-ordination compound and thus render the metal inactive. The term sequestering agents has been applied to chelating agents but this infers that the metal has been removed and not merely inactivated. 

Copper sulfate is used to control protozoan fish ectoparasites including Ichthyopthirius, Tri-chodina, and Costia. The effectiveness of the treatment diminishes with increasing total alkalinity and total hardness of the water (Straus and Tucker 1993). Copper compounds now used to control protozoan parasites of cultured red drum (Sciaenops ocellatus) include copper sulfate, copper sulfate plus citric acid, and chelated copper compounds (forms of copper bound by sequestering agents, such as ethanolamine) chelated copper compounds are considered less toxic to fish than copper sulfate and at least as effective in controlling parasites (Peppard etal. 1991). 

Chelating agents arc being used in increasing amounts for a number of important purposes. These uses may be put into two important categories first, artificial trace metal carriers and, second, sequestering agents. 

Generally, sequestering agents produce chelates with a particular metal with stabilities decreasing in the following sequence250 ... 

It is to be noted that beryllium compounds are exceedingly toxic, particularly if inhaled, and great care and precautions must be taken in handling them. Chelating hydroxy- and polyaminocarboxylic adds have been studied3 as sequestering agents for Be2+. 

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