Below is a list of common terms used in the ultrapure water industry. Click on each for a brief description:
What are Ions?
Ions are divided into two groups; cations and anions. Cations have a positive charge and include sodium (Na+), calcium (Ca++), and magnesium (Mg++). Anions have a negative charge and include chloride (Cl-), sulfates (SO4--), and bicarbonates (HCO3-).
How are ions removed from water?
Ions are removed from water through a series of chemical reactions. These reactions take place as the water passes through ion exchange resin beds. Cation resin contains hydrogen (H+) ions on its surface which are exchanged for positively charged ions. Anion resin contains hydroxide (OH-) ions on its surface which are exchanged for negatively charged ions. The final product of these two exchanges, H+ and OH-, form water molecules.
Separate bed reaction
When cation and anion resins are separated, reactions take place independently and are incomplete, thus only moderate ion exchange is achieved.
Mixed bed reaction
When cation and anion resins are mixed, reactions take place to their completion simultaneously exchanging both cations and anions, providing water that is virtually ion free.
How are ions measured?
Electrical conductance or resistance is measured by two in-line electrodes. Electrical current moves through water using ionic molecules as stepping stones. The fewer stepping stones, the more difficult the passage of electricity. This causes less electrical conductance and more electrical resistance. The temperature of the water also affects its conductivity/resistivity. Thornton electrodes and meters automatically compensate for water temperature to ensure accuracy.