Trace analysis with Hanging Mercury Drop Electrode

This experiment can be run with a VoltaLab 50 or a VoltaLab 80.

Files:
Trace analysis with HMDE.EXP
All_P.CRV
One_P.CRV
Three_P.CRV
Five_P.CRV

Specification of the test : Pb/Cd in 0.1 M HCl
Working Electrode : Mercury drop (HMDE)
Reference Electrode : Ag // AgCl
Auxiliary Electrode : Pt

The Potentiostatic Universal Differential Pulse method can be used to detect Cadmium and Lead at ppm level. A Hanging Mercury Drop Electrode (HMDE) is used in combination with a differential pulse measurement. This combination corresponds to a "stripping analysis". During electrolysis at a set potential, Pb 2+ and Cd 2+ are reduced and amalgamated on the hanging mercury drop. The determination is then performed by potential scanning in the anodic direction. The amalgamated metals are stripped back into the solution in their ionic form. The resulting stripping current is proportional to the concentration of the metal ions in solution.

* Reagents
(1) Supporting Electrolyte: 1M HCl.
(2) 1000 mg/l Pb(II) stock solution.
(3) 1000 mg/l Cd(II) stock solution.
(4) 100 mg/l Pb(II) -10 mg/l Cd(II) standard solution.

* Standard solution preparation
Add 10.0 ml 1000 mg/l Pb(II) solution,
1.0 ml 1000 mg/l Cd(II) solution and
10.0 ml of 1M HCl Suprapur in the same flask. Dilute to 100 ml with deionised water.
Always use reagent grade chemicals for reagent preparation.

* Apparatus
- MDE150 Polarographic Stand
- VoltaLab 80 (PGZ402 & VoltaMaster 4)
See Connecting a MDE150 to a PGZ402

* Electrodes
- TR020 Reference Electrode
- TM010 Platinum Electrode
- MDE/CAP 70 µm Capillary

The "Run External Unit" method is used to control the MDE in order to organise the purge, the blanketing, the stirring and the mercury drop itself.

Settings – Calculation

The " Standard addition " methods calculates quantitative results for Cadmium and lead concentration.

Curve examination : Quantitative analysis

The " Standard addition " calculation methods calculates the concentration and prints automatically the results.

The printed report indicates the correlation factor and the location of every file used for calculation to ensure tracability.

Curve examination : individual spectrums

The curves were automatically smoothed and the peak analysis was automatically performed with the appropriate "Tools" methods. The peak potential can be compared to the half wave potential given by [1]. The signals increase linearly with the concentrations. It is also possible to overlay the curves and to perform peak

Conclusion

Standard addition method can be used to perform trace analysis with VoltaLab. The metals are detected and the peak analysis provides both qualitative (half wave potential) and quantitative information (peak height) on the metal present.

[1] Electroanalytical Stripping Methods - Kh. BRAININA and E. NEYMAN