Deionized (DI) water is water that has had its mineral ions removed, such as cations from sodium, sodium, iron, copper, and anions such as chloride and bromide. Deionization is a physical process which uses specially-manufactured ion exchange resins which bind to and filter out the mineral salts from water. Because the majority of water impurities are dissolved salts, deionization produces a high purity water. Deionization does not significantly remove uncharged organic molecules.
De-ionized water is available in several Grades or Types each of which has limits on the amount and type of compounds in the water after treatment. When the de-ionized water is analyzed for compliance with the standards several parameters are tested and listed on a Certificate of Analysis representing the lot of water produced. VOCs are a group of compounds that are included in the Total Organic Carbon (TOC) category on the Laboratory Certificate of Analysis. TOC includes a variety of organic compounds including Acetone, MEK, MTBE and others. A typical Certificate of Analysis for Reagent or ASTM Type I or Type II does not break out individual VOC concentrations.