Type 1 water represents the highest grade of purified water available, often called “Ultrapure Water.” It is virtually free of ions, organic compounds, and microbial contaminants. This degree of purity is necessary for highly sensitive scientific and industrial applications where trace amounts of impurities could interfere with results or damage sophisticated equipment. Type 1 water is utilized as a chemical reagent or solvent in experiments and manufacturing processes, but it is not intended for human consumption.
Technical Specifications for Type 1 Purity
The purity of Type 1 water is defined by measurable metrics formalized by organizations like the American Society for Testing and Materials (ASTM D1193), the International Organization for Standardization (ISO 3696), and the Clinical and Laboratory Standards Institute (CLSI). The most defining characteristic is its electrical resistivity, which must reach a theoretical maximum of 18.2 MΩ·cm at 25°C. This extremely high resistivity value indicates the near-total absence of dissolved inorganic ions, as ions are the primary conductors of electricity in water.
To maintain this standard, the water must also have extremely low levels of organic contamination, measured as Total Organic Carbon (TOC). The TOC level is typically required to be less than 50 parts per billion (ppb), though some specialized applications demand less than 5 ppb. Organic compounds, even in tiny amounts, can interfere with sensitive analytical techniques or biological cultures. Specifications also control microbial contamination, requiring a bacterial count of less than 10 colony-forming units per milliliter (CFU/ml) for the most demanding grades, alongside strict limits on endotoxins and nucleases.
Multi-Stage Purification Process
Achieving Type 1 water purity requires a multi-stage purification process, often starting with a pre-treated source like Reverse Osmosis (RO) water. The initial RO step removes the majority of bulk contaminants, including 95-99% of dissolved salts and most microorganisms, protecting subsequent purification steps. The water then proceeds to a deionization (DI) stage, where it is passed through mixed-bed ion exchange resins. These resins “polish” the water by exchanging remaining inorganic ions for hydrogen and hydroxyl ions, which combine to form pure water and achieve maximum resistivity.
To address organic contaminants, the water is exposed to Ultraviolet (UV) light, often at two wavelengths. The 254 nm wavelength provides bactericidal action, destroying microbes. A second wavelength, 185 nm, is used to photo-oxidize residual organic molecules into ionizable species, which are then removed by a final passage through the ion-exchange resins. The final step involves passing the water through a 0.2 µm sub-micron filter to remove remaining particulates and bacteria immediately before dispensing. Because Type 1 water degrades rapidly upon storage, the final purification stages are typically performed “on demand” at the point of use.
Critical Uses in Science and Industry
The ultra-high purity of Type 1 water is necessary for applications where contamination would lead to inaccurate or unreliable data. In analytical chemistry, it is essential for preparing mobile phases and blanks for techniques like High-Performance Liquid Chromatography (HPLC) and Gas Chromatography (GC), where trace contaminants can produce false signals or “ghost peaks.” It is also required for sample dilution and standardization in highly sensitive elemental analysis methods, such as Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and Atomic Absorption Spectrophotometry (AAS).
In the life sciences, Type 1 water is used to prepare buffers and media for molecular biology applications, including Polymerase Chain Reaction (PCR) and DNA sequencing. The absence of nucleases and other biological contaminants is paramount to prevent the degradation of genetic material. This purity is also the standard for preparing cell culture media and reagents for mammalian cell culture and in vitro fertilization (IVF), as cell lines are highly sensitive to endotoxins and trace metals. Beyond the laboratory, water of this purity is used extensively in the microelectronics industry for rinsing delicate components during semiconductor manufacturing, where microscopic particles can cause device failure.