ISO 11852:2017

Overview

ISO 11852:2017 specifies a standardized titration method to determine the magnesium content of field natural rubber latex. The method applies to field latex preserved with ammonia (or ammonia plus formaldehyde) and measures the total divalent alkaline‑earth ions remaining after sludge removal - reported as magnesium content. The procedure is designed for routine laboratory quality control and interlaboratory comparability.

Key topics and technical requirements

• Scope: Titrimetric determination of magnesium in field natural rubber latex; applicable when ammonia content on titration is ≥ 0.2% of the latex.
• Principle: Centrifuge field latex (2 500–5 000 m/s², i.e. 250–500 g) for 3 minutes, remove sludge, dilute supernatant and titrate with standardized 0.005 M disodium EDTA (EDTA·Na2) using Eriochrome Black T indicator in a buffer at pH ~10.3–10.5.
• Apparatus: laboratory centrifuge and tubes, pH meter, burette (ISO 385 compliant), class A pipette (ISO 648 compliant), balance (0.1 mg accuracy), beaker.
• Reagents and buffers: standard magnesium sulfate solution for EDTA standardization, 0.005 M EDTA·Na2, Eriochrome Black T indicator (mixed with NaCl/KCl), and an ammonium chloride / ammonium hydroxide buffer (pH ≈ 10.5). Note: borax buffer was replaced due to health concerns.
• Procedure controls: duplicate determinations from homogenized samples; repeat if duplicates differ beyond specified limits. Endpoint color change: red → permanent blue.
• Calculation & reporting: Magnesium expressed as % (wMg) or mg/kg using the standardized EDTA concentration, titrant volume and sample mass (formulas provided in the standard). Report the average of duplicates with specified rounding.
• Precision: Repeatability and reproducibility values were established by an interlaboratory study and are provided in Annex A.

Applications and users

• Who uses it: rubber industry QC laboratories, raw material testing labs, manufacturers of natural rubber products, research laboratories, certification bodies and procurement/specification engineers.
• Practical uses: incoming latex acceptance testing, process control for latex handling and preservation, comparison of field latex quality between suppliers, and data for formulation or downstream processing where divalent ion content affects coagulation, stability or product properties.
• Advantages: straightforward titration using common lab equipment (centrifuge used for desludging), minimal extra reagents, and clear end‑point detection after sludge removal. Caution: method may not be valid for latex preserved with certain additives (e.g., TMTD or ZnO).

Related standards

• ISO 385:2005 - Laboratory glassware - Burettes
• ISO 648:2008 - Laboratory glassware - Single‑volume pipettes

Keywords: ISO 11852:2017, magnesium content, field natural rubber latex, titration method, EDTA titration, Eriochrome Black T, centrifugation, ammonium chloride buffer, latex quality control, precision.