Mercury

Hg²⁺

The ELIT mercury electrode requires highly acidic conditions (pH 0–2) for operation, making strict ISAB addition mandatory for all measurements. Critical for environmental contamination monitoring.

Cation (+)ELIT 8251Valence: Divalent

Safety Warnings

Mercury compounds are highly toxic — handle with appropriate PPE and dispose of waste according to local regulations.
This electrode has an extremely narrow and low pH operating range (0 to 2) — ISAB is mandatory for ALL samples.

Electrode Specifications

Model

ELIT 8251

Membrane Type

Solid-state crystal membrane

Ion Type

Monovalent cationDivalent cation

Molar Mass

200.59 g/mol — 1000 ppm = 0.005 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

0.2 to 20,100 ppm (1×10⁻⁶ to 0.1 Molar)

Electrode Slope at 25°C

26 ± 3 mV/decade

pH Range

pH 0 to 2

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 lithium acetate (ELIT 003). Outer filling solution: 0.1M CH₃COOLi.

ISAB / Buffer

0.1M HNO₃ — 1:1 v/v (mandatory — add 50% by volume to all standards and samples).

Standard Preparation

Dissolve 1.708g mercuric nitrate monohydrate (Hg(NO₃)₂·H₂O) in 1 litre deionised water.

Typical Applications

Environmental Monitoring Industrial Effluent Monitoring 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
Silver (Ag⁺) / Sulphide (S²⁻)	very high	All poly-crystalline membranes — unreliable in presence of Ag or S ions.

Standard Analytical Method

Apparatus Required

Ion-Selective Electrode: ELIT 8251
Reference electrode: Double junction lithium acetate (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 Hg solutions. ISAB is mandatory — add 50% by volume 0.1M HNO₃ to ALL standards and samples before measurement.

Sample Preparation & Measurement

Take 25 ml sample and add 25 ml of 0.1M HNO₃ ISAB before measurement. ISAB addition is essential to maintain pH within the narrow 0–2 operating range.

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 extremely low and narrow pH range (0 to 2) — the most restrictive of all ELIT ISEs.
ISAB (0.1M HNO₃) must be added 1:1 to all standards and samples — this is not optional.
Divalent cation — slope ~26 mV/decade.