Although water is the most commonly used laboratory solvent, the importance of water quality is often overlooked. Achieving water of sufficient quality requires the careful use of purification technologies and a method for accurately measuring and monitoring contaminants. Once pure water has been produced, it must be validated and then carefully stored and maintained to ensure that its quality does not deteriorate.
There are several commonly used methods for purifying water. The principal methods used for laboratory purposes include:
- reverse osmosis
- ion exchange
- ultraviolet (UV)
The French cleric Jean-Antoine Nollet made the important discovery that water naturally diffuses from a dilute to a concentrated solution. This phenomenon later became known as osmosis. During the following century, the study of osmosis became of particular interest to practitioners of the biological and medical sciences.
Robert Barnstead, a master plumber, developed the first all-metal laboratory distillation unit for Massachusetts General Hospital.
Bechold published a paper on the process known today as ultrafiltration. Bechold described driving solutions at high pressures through a membrane prepared by impregnating filter paper with acetic acid. He used the term ultrafilter to describe a collodion membrane of graded pore size. Ultrafiltration is now commonly understood to mean a process that allows colloidal particles, emulsions and microorganisms to be removed from a solution.
The use of ultraviolet (UV) light treatment was first attempted in the United States as a method to purify drinking water.
The Sartorius Company in Germany began selling ultrafiltration and microfiltration membranes, manufactured using the Zsigmondy process developed in 1918. This marked the beginning of the membrane market. At this stage, membranes were targeted for laboratory rather than industrial use.
Key research was performed on the phenomenon of reverse osmosis by various researchers including Michaels, Manegold and McBain.
The original patent on mixed-bed ion exchange resins was issued to Francis McGarvey and Robert Kunin. McGarvey and Kunin discovered that a mixed bed of quaternary ammonium anion-exchange resins and existing hydrogenexchange cation-exchange materials was able to effectively and efficiently remove salts from water, and could be regenerated after use. The ion exchange process, in which water percolates through a bead-like resin, is now a common method for water purification. This process is used for both water softening (in which sodium ions are used to replace calcium or magnesium ions in the water) and deionization.
Electrodeionization (EDI) was first described in a publication by scientists at Argonne Labs as a method for the removal of trace radioactive materials from water. In the process of EDI, ionizable species are removed from liquids using an electrical potential across an electrically-active medium to affect ion transport. Unlike other water purification techniques, EDI does not require the use of caustic or acidic chemicals.
The first patent for EDI was granted to a Dutch company. A U.S. patent for the purification of acetone using EDI was also granted in this year to Paul Kollsman for his Method and Apparatus for Treating Ionic Fluids by Dialysis.
The first pilot EDI device incorporating mixed resins was developed in the United Kingdom by the Permutit Company on behalf of the Harwell Atomic Energy Authority.
Loeb and Sourirajan, working in a research laboratory at the University of California, Los Angeles, succeeded in developing an anisotropic membrane that was sufficiently selective and water permeable to be able to allow desalination. The Loeb-Sourirajan film consisted of a cellulose acetate gel (~50% water), which relied on a dense layer, approximately 0.1 micron thick, for its separation capacity. It is at this exceptionally thin skin where the actual water transport and desalination takes place. This film was recognized as an important breakthrough and marked the start of the mass manufacture of asymmetric membranes for reverse osmosis.
Millipore introduced the Super-Q water purification system, designed to produce ultrapure water by providing the final polish to water pre-treated by reverse osmosis, distillation or deionization.
Cadotte and Lonsdale developed composite membranes for reverse osmosis. Cadotte later discovered how to make more effective, multilayered-polyamide reverse-osmosis membranes, now called thin-film composite (TFC) membranes, which have since largely replaced cellulose acetate membranes.
Forbes introduced the first industrial application of ultrafiltration in electrophoretic painting.
Millipore introduced the Milli-Q water purification system, the worlds first lab-scale ultra-pure water system. Milli-Q water refers to water that has been purified and deionized to a high degree by this system.
EDI devices and systems were first fully commercialized by a division of Millipore.
Millipore introduced systems with A10 monitors for Total Organic Carbon (TOC) measurement of purified water. It is known that even relatively low TOC levels in purified water affect the outcome of many laboratory experiments. Previously, water systems had measured ionic contamination by resistivity alone.
Millipore introduced ready-to-use water system validation packages for the pharmaceutical industry.
Thermo Fisher Scientific, then know as Barnstead-Thermolyne, introduced the NANOpure DIamond, the first ultrapure water system to integrate volumetric dispensing into the unit, allowing users to automatically dispense set amounts of water from the unit to eliminate spill and contamination risks.
Thermo Fisher Scientific, then know as Barnstead International, introduced the AccuDIspense, the first remote dispenser for ultrapure water systems that displays water quality at the dispensing gun, allowing users to place water systems out of site for increased workspace in the laboratory.
Millipore introduced the Milli-Q Advantage system that could be equipped with up to three Q-POD remote dispensers to deliver water wherever it was needed in the lab and remove critical contaminants at the point of water delivery without recontamination.
Millipore introduced the Milli-Q Integral water system. This was the first system to purify tap water to type 2 and type 1 levels in a single, space-saving system.
ELGA LabWater launched the PURELAB flex water purification system integrating in-hand monitoring and accurate, pure-water dispensing in one product.
THE FUTURE OF LABORATORY WATER PURIFICATION SYSTEMS
Water purification has come a long way in a short time since the first filtration and membrane systems of the twentieth century. New advances continue to drive the industry forward, such as Millipore’s Millitrack remote monitoring software that enables electronic archiving of water quality records. There seems little doubt that this pace of change will continue into the immediate future. Many experts predict that nanotechnology will become the standard of laboratory, industrial and domestic water treatment in the years ahead, potentially offering less expensive and more effective water purification methods.