January 10th, 2020 | by Micaela Scobie | Immune Diagnostics, Co.
Especially in the developed world, water quality can be taken for granted. Yet whether at home or in the lab, it is important to consider the varying degrees of water purification. To prevent equipment degradation or assay variability, reagent grade water should be used in a lab setting. Here we will briefly discuss the composition of water, why that is important, and methods of water filtration.
Water and its importance
Due to its polarity and hydrogen bonding, water can dissolve more substances than any other solvent. This is important because the high reactivity of water increases the likelihood of contamination. Thus, interaction of water with lab equipment or analytical application should always be considered.
Besides the hydrogen and oxygen molecules that compose the structure of water, other substances such as sodium, calcium, chloride, microplastics, and microbial by-products may also be found in tap water, which can affect water hardness, pH, or even biofilm production. Although the level of water purification required depends on application, all lab processes that require high accuracy and precision can be negatively affected by water contamination.
Choosing the right water for the job
For most labs, deionization of water is a baseline purification step. Ionic water purity can be assessed by resistivity/conductivity. Resistivity is defined as resistance to electrical current per unit length, while conductivity is the reciprocal of resistivity. Because electrical current is transported through water via ions, as water purity increases, conductivity decreases. At a reference temperature of 25 °C, deionized (DI) water should have a resistivity of 18.2 mega-ohm and conductivity of 0.055 microsiemens.
Aside from deionization, there are many different filtration methods to reach the appropriate water purity level for your specific application. These methods include:
- Deionization (DI)
- UV Oxidation
While use of DI water is standard in the lab, other additional methods to determine total organic carbon or microbial levels should be employed if required by the end point of use. Additional stringent requirements for water purity are appropriately placed on pharmaceutical applications. To help you decide what water purification level is right for your use, you can refer to several great resources from the NIH and USP.