Barium

Ba²⁺

The ELIT barium electrode requires a unique still-solution measurement protocol and Standard Addition for samples with high ionic strength, due to interference from common ISAB constituents.

Cation (+)ELIT 8081Valence: Divalent

Electrode Specifications

Model

ELIT 8081

Membrane Type

Solid-state PVC polymer matrix membrane

Ion Type

Monovalent cationDivalent cation

Molar Mass

137.327 g/mol — 1000 ppm = 0.007 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

0.5 to 13,700 ppm (4×10⁻⁶ to 0.1 Molar)

Electrode Slope at 25°C

21 ± 3 mV/decade

pH Range

pH 3 to 10

Temperature Range

0 to 50°C

Response Time

< 10 seconds (90% response)

Potential Drift

< 3 mV/day in 1000 ppm (8 hours)

Reagents

Reference Electrode

Single junction AgCl (ELIT 001).

ISAB / Buffer

NONE — the barium electrode is interfered with by the most common ISAB constituents. For high ionic strength samples, use the Standard Addition or Sample Addition method.

Standard Preparation

Dissolve 1.779g barium chloride dihydrate (BaCl₂·2H₂O) in 1 litre deionised water.

Typical Applications

Environmental Monitoring Industrial Process Control Water Quality Monitoring Research

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 Ion	Selectivity Coefficient	Notes
Strontium (Sr²⁺)	0.09	Highest interferent — unlikely in most samples.
Potassium (K⁺)	0.02	Significant error if K > 10× Ba concentration.
Sodium (Na⁺)	0.02	Significant error if Na > 10× Ba concentration.
Magnesium (Mg²⁺)	0.006	Tolerated up to ~20× Ba concentration.
Ammonium (NH₄⁺)	0.003	—
Calcium (Ca²⁺)	0.002	Tolerated up to ~50× Ba concentration.
Lithium (Li⁺)	0.002	Tolerated up to ~50× Ba concentration.

Standard Analytical Method

Apparatus Required

Ion-Selective Electrode: ELIT 8081
Reference electrode: Single junction AgCl (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

For low ionic strength samples, use Direct Potentiometry with full calibration (1, 10, 100, 1000 ppm Ba). For high ionic strength, use Standard Addition: calibrate to find the slope, then enter slope and expected concentration into the software.

Sample Preparation & Measurement

Measurements must be made in still (unstirred) solutions. After immersion, manually swirl beaker for ~30 seconds, then leave to stand. Record mV at the lowest point before values start to rise again (typically < 2 mins for 10 ppm and above; up to 5 mins for < 1 ppm).

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

Unlike most ISEs, barium MUST be measured in still (not stirred) solutions.
No ISAB is recommended — common ISAB constituents (K, Na, NH₄) interfere with the barium electrode.
Divalent cation — slope (~21 mV/decade) is slightly lower than a pure Nernstian response for a divalent ion.