Colorimetric Test Kits

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Detection using field test kits are very common and are used extensively to monitor arsenic in groundwater. This method of detection is based on the "Gutzeit" method which is developed over 100 years ago. Besides using it for detection in water samples, it can also be applied to testing solid waste and soil by acid extraction or acidic oxidation digestion of the sample.



The following illustrates the procedures of the “Gutzeit” method :

1. treat the water sample with a reducing agent that transforms the arsenic compounds present in the water into arsenic trihydride (arsine gas).

2. Arsenic is separated from the sample

3. The arsenic trihydride diffuses out of the sample where it is exposed to a paper impregnated with mercuric bromide.


AsH3 + 3HgBr2 → As(HgBr)3 + 3HBr

The white mercury(II) bromide will turn yellow, brown, or black if arsenic is present in the sample


4. The reaction with the paper produces a highly colored compound.

5. The concentration of the arsenic can be approximated using a calibrated color scale.



This method of detection has several pros and cons as shown below.


Advantages:

• inexpensive
• minimally trained personnel can readily perform it and read the results in the field.

Disadvantage:

• sulfur, selenium, and tellurium compounds have the potential of interfering with this assay.