Lead
Pb²⁺The ELIT lead electrode is designed for direct lead determination in environmental and industrial water samples. Stirring during measurement enhances sensitivity at low concentrations.
The Selectivity Coefficient (SC) represents the approximate apparent increase in the measured concentration caused by 1 unit of the interferent. Effect (% error) = (interferent concentration × SC / analyte concentration) × 100.
| Interfering Ion | Selectivity Coefficient | Notes |
|---|---|---|
| Silver (Ag⁺) / Sulphide (S²⁻) | very high | All poly-crystalline membranes — unreliable in presence of Ag or S ions. |
| Copper (Cu²⁺) | very high | Can only be tolerated at very small concentrations relative to Pb. |
| Iron (Fe²⁺ and Fe³⁺) | very high | — |
| Mercury (Hg²⁺) | very high | — |
| Cadmium (Cd²⁺) | >1 | Causes significant positive error if present at > one tenth the lead concentration. |
Apparatus Required
- Ion-Selective Electrode: ELIT 8231
- Reference electrode: Double junction lithium acetate (ELIT 003n)
- Dual electrode head (ELIT 201)
- ELIT Computer Interface/Ion Analyser, or Ion/pH/mV meter
- 150 ml polypropylene beakers, 100 ml volumetric flask, 1, 2, 5, 10 ml pipettes
Calibration
Calibrate with 1000, 100, 10, 1, 0.1 ppm Pb solutions. Add 2 ml ISAB to 100 ml of each standard and sample. Stir with a magnetic stirrer at ~50 rpm during measurement.
Sample Preparation & Measurement
Add 2 ml ISAB to 100 ml sample. Stir with magnetic stirrer during measurement. Wash electrodes between samples and allow 2–3 minutes stabilisation.
Results
Results are displayed as ppm and mol/l. If buffer solution has been added equally to standards and samples, figures will not need adjusting as all are affected by the same dilution factor. Allow 2–3 minutes stabilisation after electrode immersion. Wash and dry electrodes between samples to avoid cross-contamination.
- Note narrow pH range (3 to 7).
- Best results obtained in stirred solutions (unlike most ISEs).
- Divalent cation — slope ~26 mV/decade.