Introduction
The metals content in a sample of water (for instance, Mg, Na, Pb, Fe, Zn, etc.) is a significant determinant of the quality of the water and its suitability for drinking purposes. This page outlines the protocol that can be followed to determine metals content, with a focus on the preparation required in order to run the test and how it is done at Analytical Services Unit (ASU) at Queen's University in Kingston, Ontario.
Analyses performed
- Total metals digest - at the ASU, this will analyse the "30 Element Suite" of the following metals:
Ag, Al, As, B, Ba, Be, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Mo, Na, Ni, P, Pb, S, Sb, Se, Sn, Sr, Ti, Tl, U, V, Zn
Instruments and materials
- Total digest performed at the ASU with a DigiPrep digestion block with a digital controller
- Samples are then analyzed at the ASU with a Varian Vista AX CCD Simultaneous ICP-AES
- 50 mL inert polymeric containers - one per sample
- 1.0M nitric acid
Note: The above materials are those that a student might have to work with at the ASU. For a complete list of materials used in the method suggested by in the Environmental Protection Agency Method, see EPA Method 3052.
Procedure
Calibrating pipettes
1. Set the pipette volume to 1500
2. Place a small container at the center of the analytical balance and press "TARE"
3. Withdraw a sample of deionized water with the pipette
4. Add the water to the small container on the analytical balance
5. If the mass displayed is within the defined boundaries of 0.1489g and 0.1510g, the pipette is sufficiently calibrated
Preparing samples for digest
1. In case the metal has not completely dissolved in the solution, the sample must first be mixed with concentrated nitric acid (1.0M):
- Add 25 mL of completely mixed sample to an inert container
- Add 2 mL of acid to the sample
- Repeat for all samples
2. Place all the samples, without a cap, inside an incubator set at 90 degrees Centigrade and heat for 300 minutes.
3. After the samples have been heated, they will need to be diluted again. Add enough deionized water to each sample to bring the volume to 25 mL.
4. Place a cap on each sample and submit the set to the lab technician at the ASU.
Digesting the metals
The EPA method for digesting a sample and analysing the test can be found here, as provided in the link above.
An outline of the ICP/OES analysis is provided here.
Results
At Queen's, the results will be provided in table form with control values provided. Concentrations will be provided in parts per million (ppm).