Overview
ISO 17403:2014 specifies a cyanide-free titration method for determining the magnesium content of field and concentrated natural rubber latices. The standard covers two procedures: Method A for field latex and Method B for concentrated latex. Both use EDTA titration in buffered alkaline solution with NaHS as a masking agent and Eriochrome Black T as an indicator. Results can be reported as magnesium percent of latex or percent on total solids content (TSC).
Keywords: ISO 17403:2014, magnesium content, natural rubber latex, cyanide-free titration, EDTA titration, latex testing, rubber quality control
Key topics and requirements
- Scope and purpose
- Cyanide-free determination of soluble divalent alkaline-earth ions (expressed as Mg), suitable for routine quality control of natural rubber latex.
- Two methods
- Method A (field latex): typically ~2.0 g sample diluted to 100 cm3; buffer (NH4Cl/NH4OH) to pH 10.0–10.5; add NaHS masking agent; titrate with 0.005 mol·dm−3 EDTA until colour changes from red to blue.
- Method B (concentrated latex): prepare serum by diluting concentrated latex (10 g in 10 cm3 water) and coagulating with acetic acid; use 10 cm3 serum, buffer, NaHS and EDTA titration.
- Apparatus & reagents
- Burette (50 cm graduations), analytical balance (0.1 mg), class A volumetric pipettes (ISO 648).
- Reagents include magnesium sulfate standard, 0.005 mol·dm−3 EDTA, NaHS masking agent, Eriochrome Black T indicator, ammonium chloride/ammonium hydroxide buffer (pH ≈10.5), and calcium hydroxide for safe disposal of titration residues.
- Calculations & expression
- Formulas use EDTA concentration and titrant volume with a conversion factor (24.31) to compute %Mg either on latex or on TSC.
- Duplicate determinations required; Method A results rounded to two decimal places, Method B to three decimal places (on TSC).
- Quality and reporting
- Report must reference ISO 17403, sample identification, sampling method, instruments, results and units, unusual features, deviations or incidents.
Applications and users
- Quality control laboratories in the rubber industry
- Latex producers and processors (field latex and concentrated latex)
- Raw-material testing labs and product acceptance testing
- R&D and formulation teams assessing ionic contaminants affecting colloidal stability or downstream processing
Practical benefits include a validated, environmentally safer (cyanide-free) procedure for routine magnesium monitoring, aiding product consistency and process troubleshooting.
Related standards
- ISO 124 - Latex, rubber - Determination of total solids content (TSC) (used in Method B)
- ISO 648 - Laboratory glassware - Single-volume pipettes
- ISO/TR 9272 - Referenced for precision/statistical details (Annex A of ISO 17403:2014)
For implementation, follow the standard’s stepwise procedures and reporting requirements to ensure reproducible, regulatory-compliant magnesium determinations in natural rubber latex.