The pocket colorimeter kit by Hach offers an immunoassay method to measure TPH (Total Petroleum Hydrocarbons) in soil samples – a useful indicator of petrol pollution or contamination in soil.
For areas of heavy contamination the range of the test can be extended by dilution during the soil extraction step.
The first stage in the test is to extract the TPH from the soil into a liquid, it’s the liquid which will be tested.
If it is known that the samples are heavily contaminated, you can dilute this extraction by weighing out a smaller portion of soil. The standard method states to weigh out 10g of soil and perform the extraction, but if only 1g is weighed out this will give an overall 1 in 10 dilution.
This can extend the range of the test from the standard 20 to 200 ppm to higher levels.
However it should be noted that excessive dilutions, in this or any test, can greatly affect the accuracy. Weighing 0.1g as a 1 in 100 dilution would not be appropriate, as this would simply become a measure of how accurate your weighing is!
For more information on the TPH in soil test kit, see the page here – click the “more” tab for the full instructions, including the extraction step.