ISO 13536:1995

Overview

ISO 13536:1995 specifies an established laboratory method for determining the potential cation exchange capacity (CEC) of soils buffered at pH = 8.1 and for measuring exchangeable cations (sodium, potassium, calcium, magnesium). The method uses a barium chloride (BaCl2) solution buffered with triethanolamine to saturate exchange sites, followed by displacement with a known excess of magnesium sulfate (MgSO4). Determinations are applicable to all types of air-dried soil samples and include procedures for sample leaching, extraction, calibration and instrumental measurement.

Keywords: ISO 13536:1995, soil quality, cation exchange capacity (CEC), barium chloride, triethanolamine, exchangeable cations, FAAS, ICP-AES, soil testing.

Key topics and technical requirements

• Principle: Saturate exchange sites with Ba2+ (BaCl2 buffered to pH 8.1), precipitate barium as BaSO4 by adding excess MgSO4; sites become occupied by Mg2+. Measure excess Mg to calculate potential CEC.
• Exchangeable cations: Sodium and potassium measured in the BaCl2–triethanolamine extract by flame emission spectrometry; calcium and magnesium (and optionally other metals) measured by FAAS or ICP-AES.
• Reagents and concentrations explicitly referenced: BaCl2 (1 mol/L), MgSO4 (0.0200 mol/L), triethanolamine buffer at pH 8.1. Water quality per ISO 3696.
• Sample handling: Applicable to air-dried, <2 mm sieved soils; procedures include multiple leachings, centrifugation (≈3 000 g, 10 min), controlled dilutions, blanks and calibration curves.
• Safety: Barium compounds are toxic - laboratory safety and environmental controls are required.
• Quality control: Use of blanks, calibration standards and method checks; note that organic matter or dissolved salts can affect results (organic matter may lower measured CEC).

Applications and who uses it

• Routine soil testing laboratories measuring CEC for agronomy, land management and soil fertility planning.
• Environmental laboratories assessing soil quality, salinity and ion exchange properties for remediation, construction, and regulatory compliance.
• Researchers comparing soil exchange properties across sites, evaluating nutrient availability and cation balance.
• Agronomists, soil scientists, environmental consultants and regulatory agencies that require standardized, comparable CEC and exchangeable cation data.

Related standards

• ISO 11464:1994 - soil sample pretreatment (referenced for sample preparation).
• ISO 3696:1987 - water for analytical laboratory use (quality of water used in reagents).

Use ISO 13536:1995 when you need a standardized, reproducible laboratory method for CEC and exchangeable cation analysis using BaCl2/triethanolamine extraction and instrumental quantification by FAAS or ICP-AES.