Electrical Conductivity and pH Analysis


Decontamination Process Validation

As part of our water testing offering, Isopharm Laboratories uses a robotically-automated system to test for electrical conductivity and pH. This testing is a requirement of the current HTM guidelines for instrument washers, endoscope reprocessors and sterilisers, but why are we interested in this information, and what can it tell us?

The requirement for having an acceptable level of high water purity will make sense to anyone in the context of a medical environment: We do not want to introduce any potentially harmful contaminants into a patient’s system via the endoscopes and instruments used during the procedures, and therefore we must make sure that the water and steam used to clean these items is to a sufficiently high purity standard.

Two of the basic screening tests frequently used before more selective tests to ensure water purity are analysis of electrical conductivity and pH:

Electrical Conductivity

Pure water is in fact a very poor conductor of electricity, because it exists in solution as electrically neutral molecules. The H2O molecules carry no electric charge and therefore in completely pure water there are no ions in solution to carry charges, so it is the impurities that water contains which allow the conduction of electricity.

This means that electrical conductivity (EC) increases with increasing total dissolved solids content, which in turn indicates increased concentration of various contaminants such as salts, metals, sulphates, and other ions. Therefore, measured value of EC indirectly indicates the level of contamination in the water sample, and the exact nature of this can then be identified by further more specific tests.

Below are typical values for common water types:

Totally Pure Water0.055
Typically Deionized Water0.1
Distilled Water05-3.0
Reverse Osmosis Water50-100
Domestic ‘Tap’ Water500-800
Potable Water1,055 Max
Sea Water56,000 Max
Brackish Water100,000

pH (aka Degree of Acidity)

pH is also an analyte which acts as a non-specific indicator of water quality, this time in terms of the degree of acidity or alkalinity of the water being tested, with a low pH value of 1 being a very strong acid, and a high pH value of 14 being a very strong alkaline.

Pure water is neutral on this scale, with an expected value of pH 7, while drinking (potable) water and natural water exhibits a pH range because it contains dissolved minerals and gases: Surface waters typically range from pH 6.5 to 8.5, while groundwater ranges from pH 6 to 8.5.

Water with a pH less than 6.5 is considered acidic. This water typically is corrosive and soft. It may contain metal ions, such as copper, iron, lead, manganese, and zinc. The metal ions may be toxic, may leave a residue, and can stain fixtures and fabrics. The low pH can damage metal pipes and fixtures, leading to further corrosion, which can in-turn provide an environment for bacterial growth.

Water with a pH higher than 8.5 is considered alkaline. This water often is hard water, containing ions such as calcium and magnesium that can form scale deposits in pipes, resulting eventually in blockages, and with steam generators eventually failing due to the insulating effect of the scale on heating elements causing them to over-current and burn out.

Stability Time Validation

Isopharm has this year carried out stability trials to be able to increase the valid time window for your electrical conductivity samples to be tested within. The general recommendation is to take readings of pH and conductivity on-site using hand-held meters due to the analytes having theoretically low stability times.

However, our in-house validation testing has proven that accurate and reproducible results can be obtained when using our transport and analysis methods that far exceed these expectations, therefore we guarantee the validity of our results up to 5 days after sampling for pH, and have now increased our electrical conductivity stability period from 2 days to 8 days. This means you are not reliant on basic hand-held probes and can be sure of getting the most accurate results from our specialist laboratory equipment.