Many of the analytical and molecular biology applications that require the use of water include high-performance liquid chromatography (HPLC),¹ total organic carbon (TOC) analysis, sample and media preparation, rinse steps in assays, and gel electrophoresis. Different types of laboratories run experiments that require varying levels of water purity. What is needed in one lab might not be needed in another. Therefore, professional organizations have established water quality standards or guidelines to facilitate laboratory water purification within various industry sectors.

Water can be classified as Type I (ultrapure), Type II (pure) and Type III (general). Type I is typically "reagent-grade" water and used for applications requiring minimal interference and maximum precision to produce the highest-quality results. Recommended applications include atomic absorption, flame emission spectrometry, ligand assays, electrophoresis, high-sensitivity chromatographic procedures, buffer preparation solutions, standards and sample dilutions, fluorometric procedures, and other advanced analysis techniques. Type II water, commonly called "analytical-grade" water, is used for regular laboratory applications, where the presence of bacteria in purified water can be tolerated. These may include general reagents and buffers without preservatives, microbiology systems (not to be sterilized), and histology stains and dyes. Type III or "laboratory-grade" water is recommended for general, non-critical laboratory uses such as feedwater for producing higher-grade water or non-critical bacteriological media preparation. Also, filtration through activated carbon, distillation, or reverse osmosis (RO) can be used to reduce TOC levels in the water.

Regulatory needs, water quality monitoring, ease of use, space requirements, and cost are all significant issues that design engineers pay close attention to when designing a total pure water system for customers in laboratories, R&D, and manufacturing.

A well-designed total system, including storage and distribution equipment, assures that water is recirculating through the piping network at the necessary flow rates and pressures without compromising water quality. For sensitive applications, Millipore's Milli-Q or Super-Q systems are able to further polish water at points-of-use to meet specific ultrapure water requirements.

THE PURITY PRINCIPLE Although sounding like a singular term, a water purification system actually consists of several key components. The first part of the Elix and RiOs water purification systems includes the Progard TL Pretreatment Pack, which is tailored to the feed water source. It removes particulates, chlorine, and colloids from tap water to protect the next purification step — reverse osmosis (RO). Reverse osmosis then removes 95-99% of ions and 99% of dissolved organics (molecular weight >200 Dalton), microorganisms, and particles.

Millipore's reverse osmosis step includes advanced features, such as high-water recovery (for water conservation) and constant product flow rate. Typically, a standard RO-based system experiences a decline of as much as 50% in product flow rate as the water temperature decreases. With the Elix and RiOs systems, a constant flow rate from 7-30°C is always maintained. This is advantageous to researchers who can be assured that water is available in their required quantities during colder winter climates.

The Elix system further removes ionic contaminants to achieve higher water quality. It utilizes ion exchange resins, semi-permeable ion exchange membranes, and a small amount of electricity to efficiently remove ionic contaminants. Unlike conventional ion exchange or distillation, this process requires minimal quantities of water and energy, little maintenance, and no chemical regeneration or cleaning. Furthermore, the Elix modules utilize activated carbon beads within electrode compartments to effectively minimize the risk of scaling issues and to eliminate the need for additional water softeners.