Under-Recognized “Utility” Essential for Laboratory Operations
Like the late comedian Rodney Dangerfield, laboratory water purification systems get no respect. Lab workers use them every day, but few realize— beyond opening the spigot—how they operate.
“The level of knowledge in the average lab about lab water is not very high,” says Julie Akana, Ph.D., product manager for water purification products at Thermo Fisher Scientific (Asheville, NC).
Pure water is classified, in order of decreasing purity, as Type 1, Type 2, and Type 3. Culture media, clinical laboratory analyzers, and buffer preparation get by nicely with Type 2 water, which also serves as feedstock for Type 1 purification systems. Labs use Type 3 “pure” water for labware washing and rinsing and for heating and cooling devices in which mineral deposits from circulating water are a problem.
More than one method
Common techniques for water purification include distillation, filtration, deionization, electrodeionization, reverse osmosis, adsorption, and ultraviolet oxidation. Distillation is the oldest method and the broadest in terms of impurity removal, but even the best stills produce “only” Type 2 water, and reverse osmosis systems, Type 3. Stills (including double- and triple-stills) are still quite common because of their simplicity and the fact that they require no consumables.
Nick Papp, president of Aqua Solutions (Jasper, GA), describes distillation as “dead but refusing to get buried.” Negatives of distillation include high energy costs and maintenance and rapid degradation of the product.
Most single purification methods excel at one type of removal, e.g., ions, organics, or particles, and individually produce water intermediate between Type 1 and high-end Type 2. Ultrapure water systems combine several of these techniques.
For example, in a high-end ultrapure water system, tap water feeds through a reverse osmosis membrane, then into deionization cartridges, an ultraviolet cell to destroy bacteria and oxidize organics, an activated carbon cartridge to remove organic by-products of the UV step, and finally an ultrafiltration membrane to remove pyrogens and nucleases. Customers can usually mix and match techniques according to their needs.
Most of Thermo Fisher’s water system customers use Type 1 or Type 2 water and tend to think in terms of their application rather than the official water designation that supports it. Dr. Akana admits that when she worked in the lab “we just looked for the magical 18.2 megohms on the display, and once we got it, we used it for everything.” Later she would go on to write Thermo’s definitive primer on water purification.
Because of budget cuts, institutions are moving away from centralized, shared-resource water purification systems. The paradox is that such systems are probably the most costeffective, albeit capital-intensive. As a result, business is booming for smaller units suitable for a single lab or group.
Nothing lasts forever
“Trends in pure water systems are driven by the capability of analytical instrumentation to detect lower and lower levels of contaminants,” observes Nick Papp. “We’ve essentially gone from part-per-million detection to part-per-billion, so more people are demanding purer water.”
Users, he says, should pay special attention to what they’re using the water for and what species might interfere with their analyses. For example, ion analysis requires water that is as ionfree as possible; if your lab tests for pyrogens in drug samples, water purification should focus on removing those contaminants.
Estelle Riche, Ph.D., an applications scientist at EMD Millipore (Billerica, MA) warns about “emerging contaminants” in tap water, and their potential impact on ultra-pure water used in laboratories. Emerging contaminants include common prescription and over-the-counter pharmaceuticals, caffeine, herbicides, pesticides, flame retardants, and components of personal- care products.
These compounds have been flushed down drains, both intact and in human waste, for decades. Given the sensitivity of modern analytical instrumentation, Dr. Riche wonders, “Are these contaminants making their way from the tap into the high purity water used in the laboratory?”
Many such contaminants, such as endocrine- disrupting chemicals (EDCs), are highly biologically active. Dr. Riche argues that if these are present in low-quality purified water, say type 2 or type 3, they could easily disrupt delicate bioassays involving live cells or enzymes, or DNA microarrays.
For the truly concerned, it is conceivable for EDCs and other unknown or emerging contaminants to leach from water systems themselves, particularly plastic components and holding vessels.
The take-home lesson here is to monitor water, even ultrapure water, for as many contaminants as is practical, and not take conductivity readings as the final arbiter of purity.
Given modern technology, reaching the “magic 18 megohm” reading has become relatively easy. The more ion exchange resin used, the more cycles, the purer the feed water becomes. But maintaining that level of purity is problematic. As soon as ultrapure water is dispensed, it begins to interact with its environment, picking up gases from the atmosphere and impurities from its container.
“Ultrapure water is the world’s best solvent,” says Nick Papp. “It begins degrading as soon as you stop circulating and purifying it, and as soon as you generate it, it tries to dissolve its surroundings.”
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