Quality Standards for 1-Hydroxy Ethylidene-1,1-Diphosphonic Acid (HEDP)

The quality standards for 1-Hydroxy Ethylidene-1,1-Diphosphonic Acid (HEDP) are defined by the Chinese national standard GB/T 26324-2025, which replaced the previous version GB/T 26324-2010 and takes effect on May 1, 2026.

Primary Standard: GB/T 26324-2025

This standard specifies the requirements, test methods, inspection rules, and marking for HEDP, applicable to its use as a scale and corrosion inhibitor in industrial water treatment, as well as a chelating agent in textile printing and dyeing, and an additive in daily chemicals.

Key Quality Indicators (Liquid Form, ≥60%)

The new standard has significantly tightened several technical indicators compared to the 2010 version. The main quality requirements for the common 60% liquid product are as follows:

Note: For solid HEDP products (typically ≥ 97% purity), different specification limits apply.

New Test Methods in the 2025 Standard

The revised standard introduces several important methodological updates:

Structural Identification: A nuclear magnetic resonance (NMR) method has been added to confirm the characteristic spectrum and integral area of HEDP.

Active Content Determination: The classical but cumbersome quinoline phosphomolybdate gravimetric method was removed. The potentiometric titration method (volumetric method) is now the primary method, which is faster and aligns with current industry practice.

Arsenic Content: A specific test method for arsenic has been newly added to control this impurity.

International References

For comparison, the JECFA (Joint FAO/WHO Expert Committee on Food Additives) monograph specifies for a 60% aqueous HEDP solution: Total active acid 58–62%, chloride ≤ 40 mg/kg, phosphorous acid ≤ 4.0%, iron ≤ 10 mg/kg, arsenic ≤ 5 mg/kg, and lead ≤ 5 mg/kg.