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.
Types of Pure Water from Laboratory Perspective : What Analyst Must Know
By Nilesh Patankar on April 8, 2020
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.
