Modern Water - Monitoring Division

- Colorimetric Detection of Explosives in Soil

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The Ensys Explosives kits are rapid field or laboratory colorimetric tests for the analysis of explosives in soil. The kits are based on a method developed by Dr. Thomas Jenkins at US Army Corps of Engineers - CRREL.

Using a simple acetone extraction procedure, a sample can be analysed for RDX and HMX using a colorimetric procedure utilising a reagent that forms an azo dye in the presence of nitrous acid. The result, a reddish coloured solution, is read on a spectrophotometer and a simple mathematical equation is used to determine the concentration of RDX or HMX.

Using a simple acetone extraction procedure, a sample can be analysed for TNT, TNB, and DNT using a colorimetric procedure that, in the presence of the analytes, will form Meisenheimer complexes or highly coloured compounds. The result, a reddish coloured solution, is read on a spectrophotometer and a simple mathematical equation is used to determine the concentration of TNT, TNB or DNT.

  • Quantitative results
  • Least detectable concentration: 0.7 ppm TNT, 0.8 ppm RDX
  • TNT results in 10 minutes
  • RDX results in 30 minutes
  • EPA SW-846 methods

RDX

The sample is extracted using acetone and is filtered and mixed with acetic acid. A reagent pillow containing a nitrite reagent is mixed with water and set aside. The acidified sample is then poured into a tube containing zinc and allowed to react with the zinc for exactly 15 seconds. The acidified positive sample, in the presence of the zinc, will reduce to form nitrous acid. When this solution containing a positive sample is poured into the nitrite reagent solution, an azo dye will form. A positive sample will yield a very red coloured solution due to the presence of that nitrous acid that was formed when the acidified sample and zinc were combined. The more color that is present, the higher the concentration of RDX in the sample. Samples are read on a spectrophotometer and a simple hand calculation will yield quantitative results.

TNT

The sample is extracted using acetone and is filtered into a sample cuvette using a syringe. An initial blank reading of the sample is taken using a spectrophotometer and recorded. A drop of developer solution containing tetrabutylammonium hydroxide (TBA-OH) is added to the sample. A sample containing TNT or DNT will form Meisenheimer complexes or highly coloured compounds when mixed with TBA-OH. The more colour that is present, the higher the concentration of TNT in the sample. Samples are read on a spectrophotometer and a simple hand calculation will yield quantitative results.

  • Soil
  • Water
  • Picric

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