Certain organic compounds are capable of forming coordinate bonds  with metals through two or more atoms of the organic compound; such organic compounds are called chelating agents. The compound formed by a chelating agent and a metal is called a chelate. A chelating agent that has two coordinating atoms is called bidentate; one that has three, tridentate; and so on. EDTA, or ethylenediaminetetraacetate, (⁻O₂CH₂)₂NCH₂CH₂N(CH₂CO₂⁻)₂, is a common hexadentate chelating agent. Chlorophyll is a chelate that consists of a magnesium ion joined with a complex chelating agent; heme, part of the hemoglobin in blood, is an iron chelate. Chelating agents are important in textile dyeing, water softening, and enzyme deactivation and as bacteriocides.

How one can test the strength of a sequestering or chelating agent? We can test the strength of a chelating agent by a simple method! - (Volumetric Estimation of Sequesteriing Agents)

Make a solution of Calcium Carbonate or Calcium Sulphate in distilled water. Say for example dissolve 500 mg of Analar grade Calcium Carbonate in pure distilled water of 1 liter. So you have prepared a known solution of 500 ppm of hardness. Ascertain the hardness by regular EDTA and Erchrome Black indicator method.

Now take a 10ml micro-burette and fill it with the solution of Sequestering agent. Titrate and find out the end point. If 5 ml of a particular brand of sequestering agent is required to treat 1 liter of 500 ppm water, then the Chelating value (CV) of this sequestering agent is 1. If 1 ml if enough to reach end point the CV is 5.

Normally the textile sequestering agents are supplied with CV of 1 to 3 and priced accordingly.

Some more reference about Sequestering Agents:

.Chelating agents are used to eliminate water hardness and heavy metals, such as iron and copper which can affect the scouring process. These agents bind polyvalent cations such as calcium and magnesium in water and in fibres, thus preventing the precipitation of soaps. If polyvalent ions are present, insoluble soaps may form, settle on the fabric and produce resist spots. There are four major types of sequestering agents to choose from: inorganic polyphosphates, aminocarboxylic acids, organophosphonic acids, and hydroxycarboxylic acids. The inorganic polyphosphates such as sodium tripolyphosphate and sodium hexametaphosphate are probably the best overall in that in addition to sequestering most metals they also aid in cleansing the fibres. They may, however, hydrolyze at high temperature and loose their effectiveness.

The aminocarboxylic acid types such as ethylenediaminetetraacetic acid (EDTA) are very good in that they sequester most metal ions and are very stable under alkaline conditions. They are the most used types. The organophosphonic acid types such as ethylenediaminetetra (methylene phosphonic acid) are also very effective but comparatively expensive. Oxalates and hydroxycarboxylic acids (citrates, etc.) are excellent for sequestering iron but not effective for calcium and magnesium. In order to quickly and effectively bring the chemicals to the textile material, i.e. to improve their wettability and to ensure that the fibrous impurities will be removed as far as possible, it is necessary to add surfactants with good wetting and washing/emulsifying properties. A surfactant of optimal versatility to be used for preparation, and in particular for the scouring and bleaching processes, ought to meet the following requirements.