Chlorine is one of the most commonly tested parameters in water used for haemodialysis.
Chlorine has a number of uses in renal dialysis, it is used to disinfect the water that is used as the dialysis fluid. It is also used to disinfect the tubing and machinery used in dialysis treatments. After disinfecting with chlorine, the machinery is rinsed with water, and often this water is tested to check that the residual chlorine level is not too high, and that the machinery has been sufficiently disinfected.
Residual chlorine levels are often monitored because high levels of chlorine will increase the chance of a reaction with organic matter creating toxic disinfection by-products.
Renal dialysis units invest large amounts of money trying to remove chlorine from the feedwater they use to generate dialysis fluid. The water treatment process should have removed all contaminants (including chlorine) from the water by ion exchange and carbon filtration prior to it being used to generate dialysis fluid.
This makes the testing environment particularly challenging as you are usually testing for the absence of a substance. When testing for the absence of an analyte such as chlorine, renal technologists must be aware of the limit of detection of the method they are using and the specificity of the method.
ISO 23500:2019 is widely accepted for guidance on consent limits and testing chlorine in renal dialysis water, however regulations can vary globally. According to this standard the consent limit for chlorine is 0.1 mg/L total chlorine.
The standard refers to testing total chlorine, understanding the difference between free and combined chlorine can help when deciding which test method to use. You can read more about the difference between free and combined chlorine here.
Test strips have been the standard method for measuring chlorine in many countries for many years as they are easy to use and require little investment.
However, test strips are not sensitive to chlorine, and not all brands are designed for use in renal applications where the chlorine levels are very low. This increases the chances of false negative results, with testing further complicated by the often small visible colour differences between graduations i.e. between 0 mg/L chlorine and 0.1 mg/L chlorine. Because of this, there is a requirement for more quantitative test methods that are less subjective to human interpretation and have a lower limit of detection.
DPD reagents are an alternative to test strips when measuring chlorine in water samples. When used with a photometer, the human interpretation aspect of chlorine testing is removed. In ISO 23500, the DPD colorimetric method is stated as a suitable method and is known to be used in the UK.
Online or inline chlorine meters are an alternative meter which can also be used with the DPD method for measuring chlorine in renal applications.
The detection limit of the DPD method is 0.02 mg/L. It is a quantitative test and a non-subjective method meaning it is suitable for use in the measurement of water to be used in the production of dialysis fluid.
Kemio™ is our multiparameter measurement platform. It uses a sophisticated, non-subjective electrochemical method with disposable sensors to measure chlorine concentration in a water sample. The Kemio™ method is US EPA approved, with a detection limit of 0.02 mg/L for total chlorine, which is below the consent limit of 0.1 mg/L.
14th June 2022
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