The Bleach Strength Test

A Chemical Test Method to Determine the Strength of Sodium Hypochlorite


The liquid sodium hypochlorite made by the Powell Continuous Bleach Manufacturing Plant or by other methods is produced as sodium hypochlorite (NaOCl) in the presence of excess caustic. Because consumers require differing solution concentrations, bleach manufacturers need to measure specific components of the product. Sodium hypochlorite (NaOCl), excess caustic (NaOH), and excess alkalinity (Na2CO3) are components in bleach that are routinely tested. Although this test procedure does not address heavy metals and sodium chlorate (NaClO3), a decomposition product, they should be tested at intermittent intervals and will require a qualified laboratory to perform these tests.

Comparative Sample Analysis

The test method below will provide accurate and repeatable results by the producer and consumer to ensure the product is meeting the desired specification. However, there are times when the strength of the sodium hypochlorite as tested by the manufacturer will differ from the consumer’s results. Many times these differences can be accounted for by the losses in shipping due to decomposition. However, it is difficult to know when the differences in test results are decomposition losses and when they are errors in test methods or procedures. In order for both the manufacturer and consumer to verify testing methods and decomposition losses, an easy procedure can be used to verify the accuracy and repeatability of each other’s testing method and the decomposition losses that result due to shipping time and temperature. At the time of loading, the manufacturer will take two retained 250 ml samples of the sodium hypochlorite loaded in the tank truck or shipping container. The manufacturer will place each sample in a separate insulated storage container with ice of sufficient quantity to keep the samples cold.

  • The manufacturer will retain one iced sample and send one iced sample with the shipment to be given to the consumer for testing.
  • At the time of delivery, the consumer will take one more 250 ml retained sample of the sodium hypochlorite unloaded from the tank truck and place this third sample in another insulated container with ice.

Within a few hours of the arrival of the samples to the consumer’s laboratory, the consumer will notify the manufacturer that the testing of the iced shipped samples will commence and both the manufacturer and the consumer will test each iced sample a total of three times. The consumer will also test the iced delivered sodium hypochlorite from the tank truck three times. By comparing results, both the manufacturer and the consumer will have data on the repeatability and accuracy of each other’s results and the decomposition of the product during shipping will have been established for that given delivery time and temperature.

More Information:

This article is available as a PDF. Click here to download it. For more information about Sodium Hypochlorite, visit the Technical Information section.