Overview
ISO 4907-2:2023 specifies a laboratory centrifugation test method for the determination of water content in styrene anion exchange resins in hydroxide form. The standard addresses the challenge that hydroxide-form anion resins have poor thermal stability, and therefore provides a procedure that removes external water by centrifugation, converts ionic form chemically, and measures equilibrium water content without direct high‑temperature drying of the original hydroxide form.
Key topics and requirements
- Scope: Test method for water content of styrene anion exchange resins in hydroxide form by centrifugation.
- Principle: Remove external water by centrifugation, convert the resin from hydroxide to chloride form using 1 mol·L‑1 HCl, wash excess acid with anhydrous ethanol, then determine water content by mass loss on drying at (105 ± 3) °C and by mass change on form conversion.
- Apparatus & settings:
- Centrifuge: up to 5 000 r/min; recommended removal step 2 500 r/min for 5 min.
- Centrifugal filter tube and water content analyser (specific core dimensions provided).
- Oven capable of ≥110 °C and accurate temperature control.
- Reagents: anhydrous ethanol, water (ISO 3696 grade 2), HCl 1 mol·L‑1, silver nitrate indicator, high‑temperature grease.
- Procedure highlights:
- Pre-treat and sample according to Annex A and ISO 4907-3:2023.
- Centrifuge to remove external water, transfer defined sample mass (1 g) into the water content analyser.
- Pass HCl through resin at controlled flow, wash with ethanol until chloride free (AgNO3 test), dry and weigh.
- Calculation: Water content (%) is calculated from mass differences and measured exchange capacities (total and strong-base group capacities) using the formula provided in Clause 9 and Annex B derivations.
- Reporting: Test report must identify the test material, sampling method, results, and any deviations or anomalies.
Practical applications and users
This standard is intended for:
- Ion-exchange resin manufacturers for quality control of hydroxide-form resins.
- Analytical and QC laboratories assessing resin water content and consistency.
- Water treatment and chemical process operators specifying and verifying resin properties.
- Suppliers and purchasers of styrene anion exchange resins who require standardized test data.
Practical benefits include safer, reproducible water‑content measurement for thermally sensitive hydroxide resins and consistent data for product specifications, batch release, and performance prediction.
Related standards
- ISO 4907-3:2023 - Determination of exchange capacity of anion exchange resins in hydroxide form (referenced for sample preparation and capacity measurement).
- ISO 3696 - Water for analytical laboratory use - Specification and test methods.
- Other parts of the ISO 4907 series for broader ion-exchange resin characterization.
Open preview (PDF)Plastics — Ion exchange resin — Part 2: Determination of water content of anion exchange resins in hydroxide form by centrifugation
