Type I ultrapure water is by far the purest substance used in a laboratory. This article describes the high level of purity of ultrapure water, the importance of such purity and how not to compromise this during use.

Why use type I ultrapure water?
In pharma laboratories pure water is essential. Water is used in most aspects of analysis, including preparation of samples, standards, blanks, eluants and for rinsing instrumentation. Impurities at ppb levels or lower can interact with samples, active media or system components. For example, Figure 1 shows different ways in which impurities can affect the reliability and reproducibility of ion chromatography in the short and the long term.

Maintaining purity
The purity of type I ultrapure water can easily be compromised if the water system itself is inadequately managed or the water is incorrectly handled.

To maintain purity within the water purifier, it is recommended to use a system which recirculates the water periodically through the purification technologies, such as UV photo-oxidation and ion-exchange and enables system sanitisation as required to minimise bacterial growth.

Type I ultrapure water should be dispensed when needed. Kuroki found that over 80 per cent of users did not refill their wash-bottles every day with purified water. Horikiri   found that after two days storage in glass bottles or plastic wash-bottles analysis by LC-MS showed, among other impurities, di-n-octyl phthalate present in the water from the wash-bottle at ppb levels but at much lower levels in the water from the glass bottle, (Figure 2). Contamination problems can also occur if bottled purified water is stored and reused after opening.

Conclusion
The extremely high purity of type I ultrapure water enables laboratory workers to obtain accurate results from high sensitivity analyses. This analytical accuracy is dependent, however, on the use of a well designed water purification system, easy to use water dispensing and good laboratory practise.