- Silver nitrate is a strong oxidiser and stains skin dark brown/black. Wear gloves and eye protection.
- Do not mix with organic solvents or combustible materials.
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 |
|---|---|---|
| Sulphide (S²⁻) | very high | Will give unreliable readings — must be absent. |
| Mercury (Hg²⁺) | very high | Strong interference — can only be tolerated at very low concentrations relative to Ag. |
Apparatus Required
- Ion-Selective Electrode: ELIT 8211
- 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 Ag solutions. Add 2% v/v ISAB to all standards and samples.
Sample Preparation & Measurement
Add 2 ml 5M NaNO₃ to each 100 ml sample. For best stability, measure whilst stirring with a magnetic stirrer at approx 100 rpm.
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.
- For most stable and reproducible results, mix all solutions with ISAB and measure whilst stirring at approx 100 rpm.
- Store silver nitrate standards in the dark when not in use to prevent photoreduction.
- Can also be used for halide determination (Cl⁻, Br⁻, I⁻) by measuring silver after standardised halide addition.