Overview
ISO 976:2013 defines a standardized laboratory method for the determination of pH in polymer dispersions and rubber latices (natural and synthetic) using a pH‑meter fitted with a combined glass electrode and silver reference electrode. The procedure covers sampling, electrode maintenance, calibration, measurement, expression of results and test reporting. It is also applicable to prevulcanized latex and compounds or adhesives that contain polymer dispersions or rubber latices. Note: the method’s accuracy decreases above pH 11.
Key topics and technical requirements
- Measurement principle: pH‑meter with a combined glass and silver reference electrode and temperature compensation. The instrument must provide at least 0.01 pH‑unit resolution.
- Electrode design and electrolyte: combined electrode with a chemically inert diaphragm (e.g. PTFE or glass sleeve) and reference electrolyte of potassium chloride saturated with silver chloride.
- Buffer solutions and reagents: use commercial analytical buffer solutions (commonly pH 4, pH 7 and an alkaline buffer ≈ pH 9) or prepare them per the standard; use high‑purity (ISO 3696) water for preparation and rinsing.
- Calibration: two‑point calibration with a pH 7 buffer and a second buffer ~3 pH units away (pH 4 or pH 9). Verify electrode slope (gradient) is within the specified range (about -55.6 mV/pH to -61.5 mV/pH at 23 °C).
- Procedure controls: equilibrate sample, electrode and buffers within 1 °C; perform measurements at 23 °C ± 3 °C (27 °C ± 3 °C in tropical regions); rinse electrodes between samples; repeat measurements and accept agreement within 0.1 pH unit.
- Reporting and accuracy: report mean of agreeing readings rounded to 0.1 pH unit, include test temperature and any deviations from the standard method.
- Quality/precision information: Annex A provides repeatability and reproducibility data from an interlaboratory study.
Practical applications and users
- Quality control and incoming inspection in rubber, latex and polymer dispersion manufacturing
- Formulation and stability testing of latices, prevulcanized latex products and adhesives
- Research and development labs assessing dispersion chemistry or preservative/ammonia levels
- Independent testing and certification laboratories that provide compliance testing for manufacturers
- Regulatory or procurement teams requiring traceable pH data for specifications
Related standards
- ISO 123 - Rubber latex - Sampling
- ISO 3696 - Water for analytical laboratory use - Specification and test methods
- ISO 15528 - Paints, varnishes and raw materials for paints and varnishes - Sampling
Keywords: ISO 976:2013, pH determination, polymer dispersions, rubber latices, latex pH, combined electrode, pH‑meter calibration, buffer solutions, electrode maintenance, laboratory testing.