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Resources/Ion Guides/Sodium (Glass)

Sodium (Glass)

Na⁺

The Na071 glass combination sodium electrode provides superior selectivity over K⁺ (SC 0.0006) making it the preferred choice for critical sodium determinations in drinking water, food, and pharmaceutical applications. Requires high-pH operation and a high-impedance meter.

Cation (+)Na071Valence: Monovalent
Typical Applications
Drinking Water AnalysisPharmaceutical AnalysisFood & BeverageEnvironmental MonitoringWater Quality Monitoring
Electrode Specifications
Model
Na071
Membrane Type
Na-selective glass combination electrode
Ion Type
Monovalent cation
Molar Mass
22.99 g/mol — 1000 ppm = 0.0435 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
0.023 to 23,000 ppm (1×10⁻⁶ to 1 Molar)
Electrode Slope at 25°C
56 ± 5 mV/decade
pH Range
pH 10 to 14
Temperature Range
20 to 40°C
Response Time
< 30 seconds (90% response)
Potential Drift
< 2 mV/day in 100 ppm (8 hours)
Reagents
Reference Electrode
Internal reference — this is a combination electrode (reference built-in).
ISAB / Buffer
4M NH₄Cl/NH₄OH buffer (pH 10) — Add 2% v/v.
Standard Preparation
Dissolve 2.542g anhydrous sodium chloride (NaCl) in 1 litre deionised water.
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
Potassium (K⁺)0.0006Far lower than the solid-state PVC electrode — the key advantage of the glass membrane.
Hydrogen (H⁺)variableEliminated by maintaining pH above 10.
Standard Analytical Method

Apparatus Required

  • Ion-Selective Electrode: Na071
  • Reference electrode: Internal reference — this is a combination electrode (reference built-in)
  • 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 ppm Na solutions in ISAB at pH 10. Allow electrode to condition for 15–30 minutes in 100 ppm Na solution before use. For complex matrices, use Standard Addition method.

Sample Preparation & Measurement

Add 2 ml 4M NH₄Cl/NH₄OH ISAB to 100 ml sample to bring pH to 10. Maintain temperature between 20–40°C. Allow electrode to reach thermal equilibrium before measurement.

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
  • The Na071 glass combination electrode offers far superior K⁺ selectivity (SC 0.0006) compared to the solid-state PVC version (ELIT 8230).
  • Requires high pH operation (pH 10–14) and must operate within 20–40°C.
  • Best choice for drinking water, pharmaceutical, and clinical samples where potassium may be present.
  • Requires longer conditioning time than solid-state electrodes.
  • Handle glass bulb with care — rinse with deionised water after use and store in 100 ppm Na solution.
  • High DC resistance (< 250 MOhm) — use a high-impedance meter capable of handling glass electrode resistance.