Lab water purification

For most application within a laboratory environment, the quality of domestic tab water is not sufficient. Think about the presence of high concentrations of ions, organic materials, particles (colloids) and micro-organisms. All these contaminants can influence the results of your analysis within the lab. A lab water system is a system that purifies water to the desired quality for your application by combining different purification techniques. For laboratory applications 3 different types of water are defined based on their purity: type I, type II and type III.

Type 3 water is also called reverse osmosis (RO) water or laboratory grade water. It is produced from tap water by applying 2 important purification techniques: pre-filtration and reverse osmosis. During the pre-filtration, the particle filters will capture all particles that have a larger dimension than the pores. Sometimes also activated carbon filters are used in the pre-filtration. These filters will capture mainly organic materials from the water by a process called adsorption. The most important component of RO systems is of course the Reverse Osmosis (RO) membrane. In this component the water is pumped through a semi-permeable membrane against the osmotic pressure. This step removes a large part of the contaminants via the waste water: ions, bacteria, colloids, organic material, pyrogens…

Typical applications for type III water are manual rinsing glassware, final rinse laboratory dishwashers, filling water baths, climate chambers, autoclaves,…

Type II water also is called EDI water, pure water, or analytical grade water. The first steps are in most cases the same as for type III water. This means that combo instruments that produce both type III and II from tab water are easy to produce. To purify water from type III water to type II water quality, in most cases 2 additional purification steps are applied: electrodeionisation and UV irradiation. The electrodeionisation (EDI) module is constructed as a resin column with a positive electrode, a negative electrode and multiple semi-permeable membranes. It will remove a very large part of the already reduced ion concentration. The UV lamp then will irradiate the water with light with wavelength 254 nm. UV light with this wavelength is very efficient against DNA. The UV light will therefore kill off all the micro-organisms and make the water sterile.

Typical applications for type II water are: buffers, pH solutions, culture media, clinical analyzers…

Type I water is also called ultrapure or reagent grade water. It can be produced by adding some additional filtration techniques on the techniques used for type II water, or it can also be produced directly from type III water. In practice for most applications, type I water is produced directly from type III water/ RO water. To produce type I water from type II or type III water, 3 additional purification steps are needed: a dual UV lamp, an ion exchange column, and a carbon filter. The UV lamp irradiates UV light at 2 wavelengths: 254 nm and 185 nm. The UV light with wavelength 254m will further kill of all micro-organisms and the UV light at 185 nm oxidize organic material without removing it. In the ion exchange column, the ion concentration will be further reduced. This column is built up from anion exchange resin and cation exchange resin. In the last step the oxidized organic material will be removed by the activated carbon filter.

Typical applications for type I water are: HPLC, GC, AA, ICP-MS, buffer solutions, culture media fur humane and animal cell culturing, reagents for molecular biology…

Analis is distributor of Rephile water purification systems in Belgium and the Netherland.