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
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.
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