Summary: Scientists use deionized water in a variety of areas from glassware washing to DNA synthesis. To provide the proper deionization system, it’s important to understand the specific needs and requirements of laboratory grade water. Laboratory water systems come in standard configurations with a variety of available options.
Every laboratory has a need for purified water. Scientists use deionized water in a variety of areas from glassware washing to DNA synthesis. While some laboratories are stand-alone businesses, many operate within a larger business. These captive labs are the quality control or research and development (R&D) centers for high-tech industries.
The laboratory water purification market includes hospitals, universities and research companies. Other markets include pharmaceutical, electronics, forensics and environmental firms. Many of these companies purchase purified laboratory grade water at significant expense, freight and storage space. Lab water purification systems are an excellent way to provide reagent grade water on demand. While there’s a vast spectrum of end-users, a similar design and approach can be applied for laboratories requiring water purification.
In order to provide the proper purification system, it’s important to understand the specific needs and requirements of laboratory grade water. Understanding water impurities that affect laboratory testing is critical to servicing this market. Aside from the conventional impurities such as suspended solids, dissolved solids and gases, laboratory water systems may have to meet specific standards for resistivity, organics, bacteria, pyrogens, and nucleases.
Resistivity is measured by passing an electrical current through the water. Resistivity is a measurement of the mineral content of the water. Lab systems should produce water with a resistivity of 18+ megohm-cm.
Organic contaminants are residuals from natural plant and animal decomposition. Organics can also be synthetic compounds from pollution. Naturally occurring compounds include tannic, humic and fulvic acids. Total organic carbon (TOC) is a measure of both natural and synthetic substances. Organics removal can be of primary concern to the scientist depending upon the nature of their work.
Bacteria is a class of microscopic organisms that reproduce by fission or spores. There are many different types of bacteria. Some bacteria are self-sustaining while others survive on non-living material. The amount of bacteria is generally measured by culturing the sample and counting the active colonies.
Pyrogens are endotoxins created from an organisms’s fragmented cell walls and are measured in endotoxin units (EU). Their presence is determined by using the limulus amebocyte lysate (LAL) test. The LAL test uses the blood of the horseshoe crab that clots in the presence of endotoxin.
Nucleases—Rnase (ribonucleases) and Dnase (deoxyribonucleases)—are enzymes that degrade DNA and RNA. The need for Rnase/Dnase free water is critical in microbiology where the test sample cannot be compromised with foreign DNA matter.
There are a few organizations within the analytical industry that provide water purification standards for laboratory use (see FYI). The College of American Pathologists (CAP) and the National Committee of Clinical Laboratory Standards (NCCLS) use a Type I, II, and III platform (see Table 1). The American Society of Testing and Materials (ASTM) uses a similar platform but with a slightly tighter specification. ASTM also provides a Biomedical Grade Water specification giving particular attention to the sterility of the dispensing port.
Making reagent grade water
Many scientists and researchers require their laboratory water to meet one of these specifications. In order to consistently achieve these levels of purity, it has become commonplace to install a point-of-use (POU) water purification system. These POU systems utilize disposable filters and cartridges to maintain water purity.
There are several areas to address when providing a laboratory water system. The first step is to determine what type of water quality is needed. Second is to determine how much of it is needed and lastly, where it’s needed. Many times, there are multiple labs in a single location. Each lab may require its own system or several labs may share the water from a single system.
Feed water is critical to system performance. Many larger facilities have a central purification system or some other form of pretreatment feeding the laboratory polishers. Smaller laboratories may need to install pretreatment or directly treat the tap water. A system run on a tap water feed may not be able to meet the most stringent water quality standards. Additionally the unit will need to be serviced more frequently. Cartridges and filters will need to be replaced more often due to the higher load on them.
A point-of-use system run with proper pretreatment will act solely as a water polisher. Polishing units are capable of producing water suitable for almost any application. Sanitization of these systems and periodic routine maintenance is critical to keep the system running properly.
Systems come in standard configurations with a variety of available options. Standard laboratory POU systems incorporate disposable filtration cartridges, a recirculation pump and a resistivity meter. The cartridges can provide a variety of filtration functions including deionization, organics removal and filtration. The pump continuously recirculates the water in the system to keep the resistivity high and to keep bacteria from growing in the system. The resistivity is displayed letting the scientist know the purity of the water. A drop-off in resistivity indicates the need to service the system.
Ultraviolet (UV) light packages are a useful option in point-of-use systems. UV keeps the system relatively free from microbial contaminants and reduces the TOC in the product water. UV is used where organics, bacteria and TOC are of primary concern.
Final filtration is also an integral part of every lab water system. Submicron capsule filters are generally the final step in the purification process. A 0.2 micron (µm) filter is most frequently used to remove bacteria before dispensing the final product water. Finer capsule filters (.05 µm absolute) are sometimes used to remove pyrogens and nucleases. Capsule filters will restrict the flow rate at which water is produced.
Scientists need well-maintained, high purity water systems in order to do their jobs properly. Servicing scientific accounts means understanding their water purification needs and being able to supply the proper products and services.
About the authors
Jon Bergman is sales manager for ARIES Filterworks, a Division of Resintech Inc. Bergman is responsible for sales of high purity water systems and related cartridge products. He was previously a sales engineer with MAR COR Services designing and selling industrial water systems. He has a bachelor’s degree in industrial engineering from Penn State University.
Larry Gottlieb is vice president of ARIES Filterworks, a Division of ResinTech Inc. Gottlieb holds a bachelor’s degree in mechanical engineering from the University of Pittsburgh. He has been involved in the water treatment industry for over 10 years and is a member of the ASTM D19 Committee on Water and the WC&P Technical Review Committee.
Both can be reached at (856) 768-9600 or www.arieswater.com