Perchlorate
ClO₄⁻The ELIT perchlorate electrode operates over a very wide pH range and offers excellent selectivity over common anions such as chloride and sulphate. Used in water monitoring and industrial analysis.
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 |
|---|---|---|
| Thiocyanate (SCN⁻) | 0.03 | — |
| Iodide (I⁻) | 0.02 | Tolerated up to the same concentration as perchlorate (~2% enhancement). |
| Nitrate (NO₃⁻) | 0.02 | Tolerated up to the same concentration as perchlorate (~2% enhancement). |
| Chloride (Cl⁻) | 0.0003 | Can be present up to 100× more concentrated before significant error. |
| Phosphate (PO₄³⁻) | 0.0002 | — |
| Acetate (CH₃COO⁻) | 0.0001 | — |
Apparatus Required
- Ion-Selective Electrode: ELIT 8061
- Reference electrode: Single junction (ELIT 001)
- 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 ClO₄ solutions. For high ionic strength samples (> 0.01 M), add 2 ml ISAB to each 100 ml standard.
Sample Preparation & Measurement
Low ionic strength: immerse in 50–100 ml sample. High ionic strength: add 2 ml ISAB to 100 ml sample and stir well.
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.
- Wide pH operating range (0 to 11).
- Nitrate can be tolerated at equal concentration to perchlorate (causes ~2% enhancement).
- Chloride can be present up to 100× the perchlorate concentration before causing significant error.