Ultrapure water

Ultrapure water is especially purified water. In contrast to conventional water as it occurs in nature and which contains, for example, minerals such as magnesium, ultrapure water contains virtually no foreign substances.

Definition

The European Pharmacopoeia provides, among other things, the following requirements for Highly Purified Water (Aqua valde purificata ):

• ĨS conductivity ≤ 1.1 / cm at 20 ° C.
• Bacterial endotoxins < 0.25 IU / ml ( equivalent to approximately 25 ng / l)
• Total organic carbon (TOC ) ≤ 0.5 mg / l
• Nitrate ≤ 0.2 mg / l

There are differences that are evident, particularly on the electrical conductivity between the quality of distilled water, demineralized water and ultrapure water. The conductivity is given in units of S / m, found in the technical jargon is almost always an indication in ĩS / cm using. Since the water molecule is an ampholyte, which can react with themselves, even ultrapure water has a low electrical conductivity. The theoretical limit is 0.055 ĩS / cm at 25 ° C, corresponding to a resistivity of 18.2 MΩcm ( mega- ohms times centimeters). In the Reinstwassertechnik the resistance of the water is mostly used as a quality feature. The value in distilled water is between 0.5 and 5 ĩS / cm at 25 ° C.

Water for analytical purposes must have ISO 3696 at 25 ° C in grade 1, a maximum conductivity of 0.1 ĩS / cm.

In water for the preparation of medicaments that are applied to the human body, at least purified water (e.g., non-sterile fluids, which are taken orally ), for parenteral (e.g., infusion ) of water for injection (WFI ) is required. In the European Pharmacopoeia for this is, among other things, the amount of the organic fractions, which may consist of cell debris and proteins regulated.

Water for steam generation in power plants with high-pressure steam generators may have a maximum conductivity of 0.2 ĩS / cm.

Production

The most common method for producing ultrapure water is reverse osmosis, rare distillation. Both methods are combined with other purification methods such as ion exchange, activated carbon filters, ultra filtration, photo-oxidation, degassing ( vacuum degassing membrane degassing ), disinfection by UV irradiation, electrochemical deionization.

Use

Ultrapure water is required in many areas. Essentially, these are the manufacture of medicaments for injection fluids, in medical research, chemical analysis, in the manufacture of computer chips or integrated circuits (ICs; see photolithography and solar cells). In water for parenteral use water is required for injections.