Types of Pure Water from Laboratory Perspective : What Analyst Must Know
By Nilesh Patankar on April 8, 2020
Laboratory grade water is usually taken for granted in a daily lab use. Since Water is the universal solvent, it is a general human tendency to use water of any grade for any application. However, real skill lies in the quality of water you select to get desired results based on your instruments sensitivity and associated applications. If desired water quality is not used then it will surely impact your analysis with undesired variations.
Using water of desired grade (quality) in your laboratory is important in order to avoid repeated work, failure of results and wastage of samples. Using a water type with an inappropriate purity level for particular application may result in economical loss as well as wastage of resources spent on research analysis. This article will provide you an overview on different types of pure water to ease your decision making on the selection of right water purification system. Laboratory Water Purity can be assessed using several key parameters such as
Conductivity : Conductivity of water is a measure of the capability of water to pass the flow of electrical current. It is directly dependent on the concentration of conductive (free) ions present in the water. In simple words, if more Ions are present, then conductivity is higher and vice versa. The unit of conductivity is microSiemens per centimeter (µS/cm). The Ideal value of Conductivity for Ultrapure water is =0.056µS/cm at 25oC.
Resistivity : The Resistivity of water is the ability of water to resist an electric current and it’s directly related to the amount of dissolved salts in the water. It means water with the high concentration of dissolved salts will have low resistivity and vice versa. It is measured in ohms (O). The Ideal value of Resistivity of Ultrapure water is =18.2 MO-cm at 25oC.
pH Level: pH level defines acidity or alkalinity. Acidic solutions have pH values between 0-6, Neutral water has a pH of 7, wherein alkaline solutions have pH values between 8-14. Please note that as per ASTM standard (D1193-06), measurement of pH in Type I, II, and III grade water is not required as these grades of water do not contain constituents in sufficient quantity to significantly alter the pH value.
Presence of Total Silica: Presence of Silica trace can be detrimental to the Industries associated with microelectronics processing. For example, In case of chip manufacturing industry, remains of the silica traces on the wafer of microchips can lead to a significant loss in the yield. In case of steam power generation deposition of silica on heat-exchange surfaces can result in the reduction of thermal efficiency. Therefore maintaining total silica (colloidal and dissolved) in purified water is very important. The presence of Total silica is measured in ppb. The Ideal value of Total silica in ultrapure water is less than 3 ppb.
Levels of Organic Compound in Water: The presence of bacteria and other organic compounds in the water can be harmful for the analytical instruments and also can negatively impact product quality. So detecting the presence of these organic contaminants and quantifying their concentration can be very helpful. But Organic compounds can exist in water in numerous forms and measuring every single compound is practically difficult. To overcome this problem, the Total Organic Carbon (TOC) content of the solution is measured. TOC is the measure of the amount of organic molecules or contaminants present in purified water. It is measured in ppb. The Ideal value of TOC of Ultrapure water is less than 50 ppb
Biological Contamination: Bacteria, viruses and other microorganisms are the biological contaminants which can cause serious issue in untreated water. The level of Bacterial presence is measured in colony forming units per milliliter (CFU/ml). Also, Endotoxin a toxic substance present in the outer membrane of gram-negative bacteria is measured in EU/ml. The ideal value of endotoxin in ultrapure water is less than 0.03 EU/ml.
Considering global acceptance on Importance of water purity, several professional organizations have established water quality standards which includes International Organization for Standardization (ISO 3696:1987), American Society for Testing and Materials (ASTM - D1193-06), US Pharmacopeia (USP) and National Committee for Clinical and Laboratory Standards Institute (CLSI). Generally laboratory reagent water is classified in to Type I, Type II and Type III grade based on its purity.
Type I water: Type I water is also known as ultrapure water and it’s the purest grade of lab water. As per the ASTM standards (D1193-06), Type I water has resistivity of >18 MO-cm, a conductivity of <0.056 µS/cm and TOC level of <50 ppb. Type I water is recommended for highly critical applications like HPLC, gas chromatography, cell culturing, tissue culturing, mass spectrometry, trace elemental analysis, biotechnology etc.
Type II water: Type II water is also referred as pure Water. As per the ASTM standards (D1193-06), Type II water has resistivity of >1 MO-cm, a conductivity of <1 µS/cm and TOC level of <50 ppb. Type II water is a recommended source of feed water to Type I system and also considered as a good choice to feed to instruments and clinical analyzers due to less calcium buildup. Type II water is generally recommended for media preparation, radioimmunoassay, sample dilution and electrochemistry.
Type III water: Type III water is primary grade water, commonly known as instrument feed water. As per the ASTM standards (D1193-06) Type III water has resistivity of >4 MO-cm, a conductivity of <0.25 µS/cm and TOC level of <200 ppb. Type III water removes 90-99% of contaminants and is produced using Reverse Osmosis (RO). Type III water is recommended for glassware rinsing, water bath filling, feeding autoclave and other non-critical laboratory applications.
To summarize, along with the water quality, other important factors such as ease of use, volume requirement, water storage, system space, cost of annual maintenance including cost of filters should be taken in to consideration while choosing Water purification system.
If you are still wondering, which water grade suits your application and looking for a cost effective water solution, then Lablink is at your help. Our team of experts can help you select the right water purification system for your application needs. Contact us to learn more about Lablink water Purification systems.