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.
Millipore's Lab Water Division has designed a complete range of water purification systems to not only produce optimal water
quality for scientific applications but also to accommodate an array of customer bases. Millipore's Elix advanced electrodeionization
system and the RiOs reverse osmosis system employ a combination of purification technologies and integrate with a centralized
system to create a total water system. The Elix systems produce Type II analytical-grade water from tap feed water and can
generate up to 4,000 L/day for a laboratory. The RiOs systems are well-suited for applications requiring Type III laboratory-grade
water and can produce up to 8,000 L/day. Water produced by the Elix and RiOs systems is ideal to use as feed water for laboratory
equipment, such as glassware washing machines, autoclaves, and clinical analyzers. It can also be used for media, buffer,
and reagent preparation.
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,
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.