Water Purification Equipments
Information on Water Purification
Pure water is essential in the lab for a variety of purposes, including preparing solutions, conducting experiments, and cleaning lab equipment. Non-purified water can contain a variety of contaminants, such as dissolved salts, minerals, metals, organic compounds, and microorganisms. Dissolved salts and minerals can alter the pH and conductivity of solutions, while metals like iron and copper can catalyze reactions and interfere with the accuracy of analytical measurements. Organic compounds, such as pesticides and herbicides, can interfere with biological experiments, while microorganisms like bacteria, viruses, and fungi can cause contamination and infection. Additionally, non-purified water can contain particulate matter and other impurities that can clog laboratory equipment and interfere with experimental procedures.
Since impurities in water can affect the precision and reproducibility of experimental results, ensuring the proper level of purity and type of water is crucial for laboratories to produce accurate and reliable results.
The following are four categories of water categorized based on their level of purity and the specific applications for which they are suitable:
Tap water. Tap water, which is also referred to as raw or potable water, is the most elementary form of water that has not undergone prior treatment or purification for use in the laboratory. It is typically contaminated with dissolved ions, salts, minerals, microorganisms, and organic compounds. Tap water is typically utilized in the lab for cleaning dirty glassware prior to further washing, cleaning the laboratory, washing excess chemicals or samples down the sink, or as the water source for producing laboratory-grade water. It should never be used for making up solutions, final cleaning of glassware, or any other application that will directly impact the accuracy of the work.
Type III water. Type III water, referred to as primary grade water or RO water, undergoes purification through carbon filtration and reverse osmosis techniques, which can eliminate up to 99% of the impurities present in the feed water. It is commonly utilized for autoclave feed procedures, preparing media, cleaning glassware, or as a source for feeding type I lab water systems.
Type II water. Type II water, also referred to as general laboratory-grade or deionized water, undergoes further refinement using a combination of reverse osmosis and ion exchange methods to achieve a resistivity of 1-15 MΩ-cm at 25°C. This level of purity is sufficient for various applications, including solution preparation, microbiological analysis, electrochemistry, and general spectrophotometry.
Type I water. Ultrapure water, also known as Type I water, is obtained through ultrafiltration processes and UV application, resulting in the highest resistivity of 18.2 MΩ-cm at 25°C. It is required for demanding applications such as mass spectrometry, molecular biology, cell and tissue cultures, and high performance liquid chromatography (HPLC).
To ensure the quality and reliability of experimental results, laboratories must be able to accurately assess and define the purity of their water supplies. This is achieved through a range of different measures, each of which provides valuable insight into the properties of the water being used.
Conductivity. One of the most commonly used measures of water purity is conductivity. This is reported as microSiemens per centimeter (µS/cm) at 25°C and is the reciprocal of resistivity. Conductivity provides a measure of a fluid's ability to conduct electrical current and is typically used when assessing water ranging from 'raw water' through to 'drinking water.' It provides a valuable, non-specific indication of the level of ions in the water.
Resistivity. Resistivity, reported as Mega-Ohms per centimeter (MO-cm) at 25°C, is related to conductivity. A high resistivity equals a low conductivity and provides a measure of the water's ionic content. Unlike conductivity, resistivity is primarily used in the assessment of ultrapure water.
Organic Compound Levels. Organic compounds can exist in water in numerous forms, making it impractical to measure each individual compound. Instead, total organic carbon (TOC) is the most useful indicator for the presence of organic impurities. TOC is measured via a process that oxidizes the organic compounds present and then quantifies the oxidation products generated. It is currently considered the closest we can get to a 'universal indicator' for the presence of organic impurities. While chromatographic techniques may be employed to determine the specifics of organic content, this is frequently considered too expensive and time-consuming for general monitoring workflows.
Biological Contamination. The presence of biological contaminants such as bacteria and other microorganisms is a common issue in untreated water. Bacterial levels are reported as colony forming units per milliliter (CFU/ml) and are kept low through filtration, UV treatment, and sterilant solutions. Following an incubation period in suitable growth media, individual bacterial species and total viable cell counts can be determined. Bacteria counts may also be monitored through the use of epifluorescence testing to rapidly detect and distinguish between dead and living microorganisms. In addition to bacteria, endotoxins produced from the cell wall of gram-negative microorganisms (reported as endotoxin units per milliliter, EU/ml; 1 EU/ml approximately equal to 0.1 ng/ml) can be assessed using standard tests based on Limulus Amebocyte Lysate activity.
Presence of Colloids. Suspended particles in water can cause turbidity, which is measured in Nephelometric Turbidity Units (NTU). Colloidal material is defined as being less than 0.5 µm in size and may contain iron, silica, aluminum, or organic materials. The Fouling Index (FI) is frequently used to estimate the potential of water to block filters under 0.45 µm filter conditions.
In conclusion, assessing and defining laboratory water purity is a complex process that involves various measures to determine the properties of the water being used. Conductivity, resistivity, organic compound levels, biological contamination, and the presence of colloids are all important factors to consider when evaluating the purity of laboratory water. Understanding these measures and their significance is essential for laboratories to ensure the quality and reliability of their experimental results.