Presumptive testing is commonly performed by monitoring the colour changes when toxicant is present in a sample. The colour testing was used in this lab to monitor the presence of heavy-metal ions. Such toxicants are commonly found in scenarios where exposure to metals, in the environment or work-place, etc., may lead to undesirable effects. Here, the transition metal ions, lead and cadmium were used for testing in various formats, all of which were based on a colour change. The colour change stems from using a ligand which coordinates to lead selectively and results in a formation of a coloured complex. The presence of lead can be measured using a paper-test, liquid test or spectrophotometer.

Video

This video (8:18) documents in detail the full process of presumptive testing using paper test, naked-eye solution test, and UV-Vis spectroscopy test for lead (II) metal ions. All tests were conducted with sodium rhodizonate which resulted in a purple colour when lead(II) was present in the sample. To ensure the selectivity of the presumptive test, the experiments were also conducted with other metal ions, such as cadmium(II) which did not result in a false positive test.

Data Sets and Worksheet

Clicking the data set link below will automatically download the Excel spreadsheet to your computer.

Data sets (experimental data) provided include:

1. lead (II) sample without sodium rhodizonate
2. lead (II) sample with sodium rhodizonate
3. sodium rhodizonate
4. buffer only

• DATA SETS: Heavy Metal Ion Lab.xslx (118 KB)

Clicking the worksheet link below will open the worksheet for this lab in a new window. You will then have the option to download the pdf file if you choose to.

• WORKSHEET: Lab 4. Heavy Metal Ion