Incoming quality control should assess each chlorine result against the chemical fraction, analytical method and reporting basis named in the purchasing specification. Total chlorine, hydrolyzable chlorine and inorganic chlorine are related measurements with different purposes. They should not be substituted or added together without understanding their definitions. For epichlorohydrin-derived epoxy resins, a low inorganic chlorine result does not establish low hydrolyzable chlorine, while a total-chlorine result does not identify which fraction dominates. Release decisions require comparable results from a representative lot sample and a method capable of supporting the specified limit.

Define the Resin and the Required Chlorine Measurement

This guide concerns incoming, unfilled glycidyl epoxy resins derived from epichlorohydrin, including bisphenol A, bisphenol F and phenolic novolac resin families.

Reactive diluents and glycidyl esters require confirmation of method scope and sample treatment. Hardeners, filled compounds, cured encapsulants and epoxy materials made through different routes should not inherit the same procedure solely because their names contain “epoxy.”

The distinction begins with chemistry. The introduction to ISO 21627 explains that epichlorohydrin-derived resins can contain inorganic chloride and several organic chlorine impurities. Easily saponifiable chlorine consists mainly of chlorine in 1,2-chlorohydrin structures associated with incomplete dehydrohalogenation. Different chemical activities require different analytical procedures.

For incoming inspection, replace an undefined “chlorine” requirement with a named test item.

The method definition belongs beside the result. A label such as “low chlorine” cannot replace it.

Match the Method to the Intended Fraction

ISO 21627 separates the measurements into three parts:

• ISO 21627-1:2009: inorganic chlorine, also called ionic chlorine, determined by direct potentiometry and expressed in milligrams per kilogram of epoxy resin.
• ISO 21627-2:2009: easily saponifiable chlorine, with results indicative of chlorohydrin groups.
• ISO 21627-3:2009: total chlorine, whose stated coverage includes saponifiable organic chlorine and inorganic chlorine.

“Hydrolyzable chlorine” on a supplier certificate still needs a method reference. ASTM D1726-11(2019), for example, addresses easily hydrolyzable chloride in liquid epoxy resins derived from a chlorohydrin and a di- or polyfunctional phenolic compound. Its Methods A and B use different determination approaches. Similar test names do not demonstrate interchangeability with an ISO procedure.

ASTM D4301-05(2019) addresses total chlorine in epoxy resins and glycidyl ethers. Its stated material scope does not make every result labelled “total chlorine” equivalent to an ISO result or a different laboratory method.

Use the complete applicable standard or controlled laboratory procedure for testing. Public scope statements help select and interpret methods; they do not provide every operational or calculation requirement.

Check What the Hydrolyzable Result Includes

A chloride titration performed after chemical treatment does not automatically represent only newly liberated organic chlorine.

Under ISO 21627-2, the resin undergoes alkaline treatment, followed by determination of chloride using potentiometric silver-nitrate titration. The procedure includes a correction for inorganic chlorine determined under Part 1. It also distinguishes the treatment of glycidyl esters from other epoxy resins.

That correction matters when comparing laboratories. Establish whether the reported figure is:

• The final corrected easily saponifiable chlorine result.
• An intermediate chloride result before the prescribed correction.
• A result from another procedure with a different definition.

Do not subtract inorganic chlorine again from a result that already includes the required correction.

Metrohm’s application note AN-T-174 illustrates a hydrolyzable-chloride determination using alkaline treatment and potentiometric titration for liquid epoxy resin. Its relevance is the connection between chemical treatment and analytical response; it does not establish equivalence between all hydrolysis procedures.

The analytical conversion also defines the evidence boundary. Chloride released during a laboratory treatment does not establish how much chloride will become available during the actual cure or service environment.

Read the Results Together Without Creating a False Mass Balance

A resin can have low inorganic chlorine and a higher hydrolyzable result because the measurements address different forms. That pattern does not, by itself, establish contamination during transport or an analytical error.

A total result can also exceed both individual results because its procedure addresses a broader fraction.

Do not calculate:

Total chlorine = reported total chlorine + hydrolyzable chlorine + inorganic chlorine

The categories overlap. Nor should subtraction be used to identify a specific remaining compound unless the methods, corrections and analytical uncertainty support that interpretation.

Use the pattern to select the next check:

If a proposed total method is intended to bound a narrower fraction, demonstrate that coverage and its suitability at the required limit. Obtain approval for the substitution before using it for release.

Make the Incoming Sample Represent the Delivered Lot

Record the resin grade, manufacturing lot, container identity, sampling point and condition on opening.

Use sampling equipment and containers demonstrated to be suitable for the measurement. Where contamination is suspected, include an appropriate sampling or container blank rather than immediately attributing the result to the resin.

If the material is nonuniform, document the condition and use an approved homogenization or sampling procedure. Unrecorded warming, solvent addition or removal of a separated portion changes the sample being evaluated.

For a supplier–buyer comparison, use traceable split samples where practical. Record whether each laboratory tested material from the original commercial container, a retention sample or a repacked bottle.

These controls establish which material the result describes. They do not require every resin to follow an identical sampling preparation.

Align Units, Sample Basis and Method Capability

Report the result on an explicit mass basis, preferably as milligrams of chlorine per kilogram of the stated material.

1.00 mass % = 10,000 mg/kg

A chloride concentration measured in an extract is not yet a concentration in the original resin. The calculation must account for sample mass, extraction or preparation volume and any dilution.

For a resin solution, distinguish results per kilogram of supplied solution from results per kilogram of resin solids. For a blend, confirm whether the result represents the complete blend or an individual component.

Method capability must also support the acceptance limit. “Not detected” means below a stated detection capability under that procedure; it does not mean zero. A reporting limit above the purchasing limit cannot demonstrate compliance.

Review the evidence relevant to the method and matrix: blank contribution, titrant standardization or calibration, repeatability, endpoint evaluation and recovery where applicable. An added chloride recovery check can assess part of the measurement chain; it does not necessarily demonstrate complete conversion of organically bound chlorine.

Investigate Disagreement Before Changing the Specification

When results conflict, first establish whether the laboratories measured the same attribute.

Compare the method edition, preparation, reaction conditions, correction, reporting basis and calculation. Then examine blanks, standardization and analytical repeatability.

For a disputed hydrolyzable result, specifically check whether both laboratories applied the required inorganic correction. If a procedure has been shortened or otherwise modified, obtain evidence supporting that modification for the resin concerned.

Repeat testing should follow the approved investigation plan. Keep the original result and document why another analysis was performed. Averaging incompatible methods or selecting the lowest retest result does not resolve the discrepancy.

If comparable testing confirms a change, investigate the affected fraction and lot history. A chlorine result alone does not identify a manufacturing fault or justify tightening every chlorine specification.

Make a Release Decision Within the Evidence

Passing chlorine inspection does not establish overall raw-material release or finished-package reliability. Other required characteristics and application qualification remain separate acceptance conditions.

ChemicalCell’s Polymers directory provides a starting point for resin-family browsing. Confirm the exact epoxy grade and its method-specific specification before using a catalogue description for incoming inspection.

For each received lot, complete one chlorine review record linking the required fraction, method, sample basis, result, reporting capability and acceptance decision. Release, hold or investigate according to that record rather than treating the three chlorine labels as interchangeable.