One of the most common reagents and considered as a universal solvent is water, therefore, it is vitally important to take care of its purity. If systematic control of the purity or quality of the water for laboratory use is maintained, the elimination of bias in the results is promoted, interference or collateral reactions are avoided and thus the reliability in said results is increased.
Water is composed of calcium and magnesium salts, which provide hardness, it also contains other substances such as iron, silica, manganese, chlorides, sulfates, sodium and other suspended materials. Water hardness is a factor that limits its use in certain processes, it is important to know the content of calcium and magnesium, because of the property they have to produce scale. There are several methods used in the treatment of water and the use of each of them depends on the objective pursued with the treated water. At present, laboratories that use water have established quality or purity requirements, as well as methods of production and analysis of water where the process or processes for purification must be established.
Water composition
The natural water cycle has different compounds that are considered impurities. These impurities present in water can be classified into three large groups:
• Dissolved Ionic (inorganic)
• Non-ionic Insoluble (organic, microorganisms, pyrogens, particles)
• Sodas
Definition of water quality
The different levels of water purity are defined according to the chemical physical parameters, such as electrical conductivity, resistivity, carbon content, oxygen or silica.
Water purification
There are different qualities of water and different needs depending on their use. In the purification there are different processes to eliminate impurities; Among the most important are:
- Filtration.
- Ultrafiltration.
- Distillation.
- Inverse osmosis.
- Adsorption with activated carbon.
- Deionization.
Distillation is the oldest method for water purification. In distillation, the water is heated to a boil and the steam is separated, counted and collected. Although some type of contamination of feedwater remains, distillation is popular because boiling ensures the death of microorganisms in a vegetative state. Water distillation consists in separating the components based on the differences in boiling points. Compounds with a low vapor pressure will have high boiling points and those with a high vapor pressure will have low boiling points. The most common types of distillation are: Simple Distillation, Fractional Distillation and Steam Drag Distillation.
What information does electrolytic conductivity give us?
Electrolytic conductivity refers to the ability of water to carry an electric current, this property is related to the total concentration of ionized substances in the water and the temperature at which the measurement is made. The measurement of this parameter is the most used to get an idea of the inorganic purity of water. One of the characteristics that define the purity of water is the electrical conductivity, a chemical physical parameter that was measured obtaining a value of (5.0 ± 0.06) μS / cm at (25 ± 1) ° C, which corresponds to Water Grade 3, according to NC-ISO 3696: 2004; which meets the necessary specifications for the preparation of the liquids or solutions involved in the process of calibration and verification of the densimeters.
Obtaining water with the correct quality for laboratories depends on the selection of the correct purification technology and a system design that accurately measures and controls impurities. Producing pure water is only part of the equation; Quality validation, water storage and system maintenance are also key to ensuring you have the quality of water that is needed. The water that must be used in the calibration laboratories according to the physical quantity to be measured is based on the quality criteria of each laboratory for the intended use.
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