(3) Sequestering agent

Water contains metal ions such as Ca (calcium) and Mg (magnesium). It is well known that the larger amount of such metal ions will hinder foaming and compromise the cleansing effect. In the industrial cleansing, these ions are also detrimental because they turn into insoluble salts after reacting with alkaline materials.
The agents used to increase the cleansing effect by deactivating these metal ions are called sequestering agents. The following types of agents are available:

(1) Inorganic sequestering agents

Polymeric phosphate-based agents are very common. Sodium tripolyphosphate is the most popular item as it is inexpensive and excels in sequestering abilities for Ca and Mg because its alkaline level is perfect for detergent additives. However, it is not so effective for trivalent ions such as ferrous ions. [Table 1] shows sequestering agents of polymeric phosphate.

[Table 1] Amount of metal ions sequestered in 100 g of polymeric phosphate (room temperature/in units of g)

(2) Organic sequestering agents

This type of agents is also called "chelating sequestering agents" because it transforms metal ions into stable compounds by retrieving metal ions to form a chelating complex (the term "chelate" came from the word meaning "crab's claw").
The following agents are available:

Hydroxycarbonates

Citric acid, glycolic acid, gluconic acid and their salts. [Table 2] shows an example of the ion sequestering amount.

[Table 2] Amount of metal ions sequestered in citric acid and gluconic acid (g)

Aminocarbonates

Nitrilotriacetic acid, ethylenediaminetetraacetate (EDTA), etc.

Hydroxy-aminocarbonates

Hydroxy-ethylenediamine tetra-acetic acid, for example.

Sequestering agents are added to alkali degreasing, boiling degreaser, and electrolytic cleaning bath and more. They form stable and inactive compounds by quickly reacting with metal ions in the cleaning solution or metal ions of the dirt particles liberated from metal products after cleaning.
In other words, the cleaning by these agents works because the metals that could hinder the cleaning effect in the solution lose their abilities to combine with other ions (metal ions are sequestered).