Part 11. Running your first arsenic measurement

Objective: quantify dissolved arsenic via stripping voltammetry and standard addition. A complete arsenic measurement normally includes at least three runs: the sample, standard addition 1, and standard addition 2. Each run should ideally contain four repetitions.

Step 1 - Create or open a sample in OpenVoltam

1. Open OpenVoltam.
2. Click New Sample or Open Sample.
3. Enter metadata such as location, date, and operator name.
4. Save the sample workspace.

Step 2 - Sample measurement in OpenVoltam

1. Click New Run.
2. Select Method: Arsenic Detection.
3. Select Device: Rodeostat.
4. Select Run type: Sample.
   1. Enter sample volume.
   2. Enter total cell volume.
5. Set repetitions to 4, recommended.
6. Click Ready to Run.
7. Double check to ensure that the setup looks good:
   1. Prepared sample is in electrochemical cell
   2. All electrodes are at least 1cm submerged in sample
   3. Electrochemical cell is centered on stir plate and has stir bar inside
   4. Electrode wires connected to potentiostat
   5. Potentiostat I/O pins connected to relay and stir plate
8. Click Begin Run.

The voltammogram will update live during acquisition. When the run finishes, data are stored automatically and voltammograms are displayed. You may analyze results immediately or close and analyze later. Immediate analysis is recommended for arsenic measurements.

Step 3 - Standard addition 1

After measuring the sample, add a known amount of arsenic standard to the same electrochemical cell. This is the first standard addition. Recommended: in a sample volume of 40 mL, add 100 uL from 1000 ppb arsenic standard to reach a standard addition concentration of 2.5 ppb.

1. Right-click the previous run.
2. Select New Run from Config.
3. Change run type to Standard Addition.
4. Enter added standard volume.
5. Enter standard concentration.
6. Add a clear note, for example: Well_A + 2.5 ppb As.
7. Confirm repetitions: 4 recommended.
8. Run the measurement.

Step 4 - Standard addition 2

Repeat the standard addition step to further increase the sample’s arsenic concentration by a known quantity Use a clear note, for example: Well_A + 5 ppb As. Clear naming prevents calculation errors later. Recommend: add the same amount as for standard addition 1.