Conductivity became a key parameter for the quality of purified water and Water For Injection (WFI) in 1996 for both the European Pharmacopoeia and United States Pharmacopeia. The conductivity of water depends on the value of the pH, the temperature of the water and on the amount of carbon dioxide. The unit for measuring the conductivity is "μS/cm". The higher the temperature, the higher the conductivity level is. Theoretically, the purest distilled water has a conductivity value of 0.0548 µS/cm at 25 °C. Water that's not as pure will have higher conductivity.
There are many different instruments for measuring the conductivity. Prior to testing, a researcher has to carefully select instruments. Several things determine the selection, such as the factors that affect measurement accuracy, format and units of reported results, suitability for the measuring environment and features assisting the ease of use. Bench-top instruments are compact, case-packed devices that have different ranges for measuring conductivity. These instruments are portable, suitable for field measurement of conductivity, resistivity and salinity.
The temperature of liquids significantly determines the level of conductivity, and changes the conductivity standards for the experiments. An increase in the liquid's temperature causes the increased mobility of ions. The Temperature Coefficient of Variation shows the increase of conductivity for a temperature change of 1 degree C. The coefficient is different for different mixtures. The temperature control helps in comparing conductivity measurements. Most measurements are referenced to 25 degrees C, but there are some experiments that require other temperatures.
Conductivity measurements are used for making critical decisions and can have a serious impact on the product integrity, human health, food safety and environmental protection. To secure precise conductivity standards, researches must comply with the principles of good laboratory practice. The measurements need to be comparable with other measurements. This is achieved by linking the results with a common reference. In order to be used, the measurements also need to be traceable and accurate. Factors that affect the choice of the conductivity standards are: use of primary and secondary standards, stability of standards, use of control standards and accreditation of the standard manufacturer.