Measuring Free Chlorine: Kemio vs DPD

In this article we use side by side testing to demonstrate some of the advantages Kemio has over DPD for measuring free chlorine.

Historically, the most popular method for free chlorine measurement has been DPD. DPD gives high levels of accuracy when analysing low concentrations of free chlorine – this makes it the ideal test for applications such as drinking water and swimming pool testing.

DPD has an upper testing limit of 5 mg/L which means that sample dilution is required to bring the free chlorine concentration within range when testing in sterilising applications. Our new Kemio FHR sensor measures up to 100 mg/L free chlorine without the need for dilution. To find out more about our new FHR sensor click here.

A side-by-side comparison of measuring free chlorine using DPD testing (with a photometer) and Kemio testing shows that the Kemio method has advantages over DPD. To find out about Kemio and how it is different from photometry watch our webinar recording here.


Advantages of Kemio

1. Faster Test Time

In applications where a high frequency of testing is required, such as fresh produce washing, a rapid, simple test method is crucial. Kemio uses a truly simple test method allowing you to save time on your testing procedures. See for yourself by watching our short instructional video here. When measuring a concentration higher than 5 mg/L free chlorine with DPD, a dilution is required which increases test time significantly.

With an expert photometric user, it was 35 seconds faster per test to use Kemio. Over 10 repeats, this would save almost 6 minutes. For a non-expert photometric user, it was 50 seconds faster to perform a Kemio test, which over 10 repeat tests could save over 8 minutes of time. Over days and weeks of testing, this adds up to a huge amount of time saved using the Kemio method.

2. Improved Accuracy of Results

As with any method, if a dilution is required, the accuracy of the test will be affected. Comparisons between both Kemio and DPD test results with and without dilution show a clear higher accuracy when no dilution is required.

Dilution is required when DPD is used to measure higher range free chlorine. The added complexity of dilution can reduce the accuracy of test results. Our new Kemio FHR sensor removes the need for dilution, ensuring consistently accurate results.

A leading salad grower carried out a trial comparing our Kemio FHR sensor to their current DPD test method.  The DPD method required a 20x dilution to bring the sample within the range of the test. The graph below shows the Kemio FHR sensor provides consistently accurate results across all tests performed.


3. Less Variability Between Operators

In most applications, it is common to have multiple operators performing testing throughout the day. Some users may be more experienced than others, and this can affect the quality of the results.

The effect of user variability on test results was investigated. Free chlorine was measured by a very experienced user and a less experienced user comparing the Kemio sensor method and the DPD photometric method. A known standard of free chlorine was measured using both methods, and 25 repeats were performed for each.

The DPD method can suffer from user error, and this is shown by the larger spread of results with a less experienced user. The accuracy can also suffer, shown by the higher free chlorine measurement. Our FHR sensor gave a mean result of 0.49 mg/L and had a small spread of results, irrespective of user.

Kemio’s simple method reduces the risk of user error and variability, ensuring consistently accurate results regardless of the user.

Measuring Free Chlorine Using Kemio FHR Sensors         

Our new free chlorine sensor can measure up to 100 mg/L free chlorine without dilution, improving the accuracy of your results. The simple method means time can be saved on testing and results are consistent, irrespective of the user.

Why should you choose Kemio Technology?

Kemio™ is different to traditional test methods, doing the hard work for the user and ensuring accurate, repeatable and reliable results each time. Kemio™ has been independently verified as the best test method for monitoring of produce wash waters, find out more here.

With Kemio™ you can have full confidence in your results and your disinfectant dosing. Program your device to your specification so that all results display a pass or fail result, giving your operator clear guidance when corrective actions are required.

Kemio™ creates a fully traceable and auditable dataset, with automatic results logging. All test results are stored on the instrument, with a time/date stamp and the ability to add further information such as operator and location. This data can then be downloaded to a PC by connecting the device through USB.

Ideal for users who use more than one disinfection type, Kemio™ Disinfection enables testing of bromine, chlorine, chlorine dioxide, chlorite and peracetic acid (PAA) on one device.

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