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Purified water is a reagent used in a variety of molecular biology experiments, for sample and media preparation, in mobile phases of liquid chromatography techniques, and in rinsing steps. The combination of several technologies in water purification systems allows delivering high-purity water adapted to each application and technique. Through a series of examples, the importance of water quality on biotechnology experiments, such as single nucleotide polymorphism (SNP) analysis by denaturating HPLC, RNA preparation and PCR, is presented. Results obtained on DNA mutation and single nucleotide polymorphism analysis using the denaturating HPLC (DHPLC) technique highlight the benefits of organic removal by UV photooxidation process. Comparative gel electrophoresis data show that ultrafiltration is as efficient as diethylpyrocarbonate (DEPC) treatment for suppressing RNase activity in water. Gel electrophoresis and densitometry measurement also point out the benefits of ultrafiltration to carry out reverse transcriptase-polymerase chain reaction quantitatively.

Recent enhancements in modern analytical instrumentation have dramatically improved the sensitivity of analysis. Trace elements are now measured at ppt and sub-ppt levels. These levels can be achieved if careful control of the analytical protocol is maintained. Contamination can result from anything that comes into contact with the sample; the laboratory environment, the air, and anything used during sample preparation. Limits of detection down to ppt levels can be achieved if special care is taken with the experimental environment as well as with the quality of the reagents. This includes the ultrapure water used to run blanks, dilute samples or prepare standards. Part of this paper looks at the most sensitive multi-elemental analytical tool, i.e. inductively coupled plasma mass spectrometry (ICP-MS). Some of the most common causes of interference will be reviewed, as well as ways of reducing this interference by specific instrument developments and particular care taken during inductively coupled plasma mass spectrometry analysis. Sub-ppt values for limits of quantification are achievable when the ultrapure water used is produced by a system for which all parts have been carefully selected and whose configuration has been specifically developed for ultratrace purposes. This specific water purification system is described and typical values that can be achieved for blanks with inductively coupled plasma mass spectrometry technology are shown.