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Resources/Ion Guides/Cadmium

Cadmium

Cd²⁺

The ELIT cadmium electrode is designed for direct cadmium determination in environmental and industrial water samples, with important limitations on co-present heavy metals.

Cation (+)ELIT 8241Valence: Divalent
Electrode Specifications
Model
ELIT 8241
Membrane Type
Solid-state crystal membrane
Ion Type
Monovalent cationDivalent cation
Molar Mass
112.411 g/mol — 1000 ppm = 0.009 M
Physical Size
130 mm body (excl. contact) × 8 mm diameter. DC resistance < 2.5 MΩ at 25°C. Min. sample volume: 5 ml.
Operational Specifications
Concentration Range
0.1 to 11,000 ppm (9×10⁻⁷ to 0.1 Molar)
Electrode Slope at 25°C
26 ± 3 mV/decade
pH Range
pH 3 to 7
Temperature Range
0 to 80°C
Response Time
< 10 seconds (90% response)
Potential Drift
< 3 mV/day in 1000 ppm (8 hours)
Reagents
Reference Electrode
Double junction (ELIT 003). Outer filling solution: 0.1M CH₃COOLi.
ISAB / Buffer
5M NaNO₃ — Add 2% v/v.
Standard Preparation
Dissolve 2.744g cadmium nitrate tetrahydrate (Cd(NO₃)₂·4H₂O) in 1 litre deionised water.
Typical Applications
Environmental MonitoringIndustrial EffluentWater Quality MonitoringResearch
Interference

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 IonSelectivity CoefficientNotes
Silver (Ag⁺) / Sulphide (S²⁻)very highAll poly-crystalline membranes — unreliable in presence of Ag or S ions.
Copper (Cu²⁺)very highElectrode cannot be used in presence of significant copper concentrations.
Mercury (Hg²⁺)very highElectrode cannot be used in presence of significant mercury concentrations.
Iron (Fe²⁺)~10Causes spuriously high values if Fe > 1/100th of Cd concentration.
Lead (Pb²⁺)~10Causes spuriously high values if Pb > 1/100th of Cd concentration.
Standard Analytical Method

Apparatus Required

  • Ion-Selective Electrode: ELIT 8241
  • Reference electrode: Double junction (ELIT 003)
  • 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 Cd solutions. For high ionic strength samples (> 0.001 M) or pH > 7, add 2 ml ISAB to each 100 ml standard.

Sample Preparation & Measurement

Low ionic strength, pH < 7: no preparation. High ionic strength or pH > 7: 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.

Analytical Notes
  • Note narrow pH range (3 to 7).
  • The ELIT 8241 cannot be used in the presence of significant copper or mercury — pre-treatment or removal is required.
  • Divalent cation — slope ~26 mV/decade.