Lab Water Purification

From routine cleaning tasks to sensitive analytical applications, water is a fundamental resource used in the laboratory. However, water purity can have a significant impact on experiments and their accuracy, making it crucial to select water with the appropriate level of purity for the application it will be used for. This infographic provides an overview of the types of laboratory water, their suitability for different applications and methods of purification. Several applications depend on high-purity water free from contaminants, and using the wrong type of water can result in a range of issues with experiment accuracy and reliability, as well as instrument safety and performance, including: However, water purification can be expensive, and using higher-purity water than is needed can incur unnecessary costs. It is, therefore, crucial to understand the type of water your application needs. • Damage to HPLC pump and injectors • Skewed results due to additional impurities, particularly for trace analysis • Interference with microbial growth • Blockages in optical sensors and fluid lines • Production of higher background values • Contamination of cell culture • Calibration sample errors • Altered pH of testing solutions THE IMPORTANCE OF WATER PURITY Despite being safe to drink, tap water can contain low levels of impurities and contaminants, such as suspended particles, ions and dissolved gases, all of which can impact experimental processes and results. TYPES OF LABORATORY WATER Three principal types of laboratory water were defined by the 1998 National Committee for Clinical Laboratory Standards Guidelines for Classification of Water Types. Although laboratory water is still commonly referred to according to these types, alternate classification systems have since been developed. DEFINING WATER PURITY Several parameters can be used to define water purity, including pH, conductivity and silica content. The exact criteria used vary between standards-setting organizations. PURIFICATION PROCESSES Laboratory water can be purified using a range of methods; the type of water needed dictates the processes and technologies used. The state of feedwater used should also be considered. MICROORGANISMS AND MICROBIAL BY-PRODUCTS including bacteria, viruses and endotoxins. DISSOLVED GASES mainly oxygen, nitrogen and carbon dioxide, with traces of inert gases. INORGANIC IONS including sodium, magnesium, calcium, iron, chloride, sulphate and nitrate. ORGANIC COMPOUNDS wide variety of compounds including lignin and humic acid. PARTICULATES can be hard, soft or colloidal. • Purest form of water produced. • Produced using UV light and ultrafilters. • Easily contaminated and must be properly stored. • Used in highly sensitive applications and analytical procedures, including chromatography, flow cytometry, molecular biology applications, atomic absorption spectroscopy and cell and tissue culture. TYPE I ULTRAPURE WATER TYPE II GENERAL LABORATORY GRADE WATER TYPE III PRIMARY GRADE WATER • High purity level. • Produced using reverse osmosis and deionization. • Used in applications including media preparation, microbiological culture, biochemical assays and as feed water for washing machines and autoclaves or for Type I production. • Lower purity level. • Produced using carbon filtration and reverse osmosis technology. • Used in non-critical basic lab applications such as glassware washing and as feed for autoclaves or for Type 1 production. • Cost-effective way to reduce contaminants. ASTM D1193-06 from ASTM International provides specifications for four types of reagent water, based on pH, conductivity, resistivity, total organic carbon (TOC), and sodium, silica and chloride content. Type I is the purest. Three sub-standards measure bacteria and endotoxins. Conductivity – how well the water can conduct electrical current. Ion levels and inorganic impurities are measured. Common measurement for raw water and drinking water. Indicates the level of ions in the water. Resistivity – how much the water resists conducting electrical flow. Indicates the water’s ionic content. TOC – indicates the presence of organic impurities. Oxidation products are measured. Often used for Type I water. pH at 298 K (25 o C) — — — 5.0 to 8.0 TOC, max, µg/l 50 50 200 No limit Sodium, max, µg/l 1 5 10 50 Chlorides, max, µg/l 1 5 10 50 Total silica, max, µg/L 3 3 500 No limit Type I Type II Type III Type IV 0.056 1.0 Electrical conductivity, max, µS/cm at 298 K (25 oC) 0.25 5.0 18.0 1.0 Electrical resistivity, max, MΩ-cm at 298 K (25 oC) 4.0 0.2 ISO 3696:1987 from the International Organization for Standardization provides specifications for three grades of water for analytical laboratory use based on pH, conductivity, oxidizable matter oxygen content, absorbance, residue post-evaporation and silica content. Grade 1 is the purest. The Clinical and Laboratory Standards Institute primarily focuses on a single standard for water for clinical laboratories – Clinical Laboratory Reagent Water. DISTILLATION • Water is boiled and evaporated into steam. • Impurities such as bacteria, organic compounds and heavy metals are removed. REVERSE OSMOSIS • Water is pushed through a semi-permeable reverse osmosis membrane under high pressure. • A range of impurities, including ions and organic compounds, are trapped and removed. • Pre-treatment is recommended to protect the membrane. ABSORPTION • Activated carbon is used to remove chlorine and chloramines. • Chlorine is reduced to chloride and carbon dioxide. • Chloramines are broken down into ammonia, nitrogen and chloride. ULTRAFILTRATION • Small pores eliminate contaminants, including endotoxins, pyrogens, enzymes and colloids. • Prone to clogging. ION EXCHANGE • Water passes through beds of ionexchange beads. • Ions such as magnesium, calcium and chloride are removed and replaced with hydrogen and hydroxyl ions, which combine to produce water. • Very effective at reducing ionic contamination. ELECTRODEIONIZATION • Combination of electro-dialysis and ion exchange technology. • Ions are removed. • Less prone to microbial contamination than ion exchange resin beds. ULTRAVIOLET OXIDATION • Water flows through a UV chamber. • Organic compounds are oxidized and removed downstream by ion exchange. • Microbial growth is also stopped. NaCl H₂O H+ OH⁻ Water purity can have a significant impact on experiments and equipment, so it is important to consider the purification technologies needed to produce the type of water suitable for your application.