Overview
ISO 6923:2023 defines a validated analytical method for the quantitative determination of monomeric diisocyanate content in paints, varnishes, adhesives and similar liquid or pasty coating products. The method uses derivatization with p‑nitrobenzyl‑N‑propylamine (PNBPA) followed by analysis with ultra high performance liquid chromatography and ultraviolet detection (UHPLC / HPLC‑UV). It covers common monomeric diisocyanates - MDI, TDI, IPDI and HDI - for concentrations from 0.01 % to 2.0 % mass fraction (with dilution recommended for higher levels).
Key topics and requirements
- Scope and targets: Quantification of 2,4’‑/4,4’‑MDI, 2,6‑/2,4‑TDI, cis/trans‑IPDI and 1,6‑HDI in various matrices.
- Sample preparation: Direct weighing (typical sample mass 30–250 mg) into a 10 mL flask, dilution with dry acetonitrile, homogenization (shaker + ultrasonic bath), and derivatization (500 µL sample + 500 µL PNBPA solution).
- Derivatization reagent: Preparation and handling of PNBPA (conversion from PNBPA‑HCl, extraction, drying and storage in acetonitrile at ≤4 °C).
- Chromatography: UHPLC/HPLC with a C18 column (e.g., 100 × 3 mm, 2.6 µm), multi‑wavelength UV detection (typical wavelengths 275 nm and 250 nm), small injection volume (2.5 µL) and a defined acetonitrile/water/sodium acetate gradient.
- Calibration and quantification: External standard calibration (six concentration levels prepared from a stock), linear fit (including origin) and summed integration for IPDI isomers. Routine use of standard sets and check standards for quality control.
- Performance range: Reliable quantification from 0.01 % to 2.0 % mass fraction; instructions for dilution and verification for higher concentrations.
- Safety and sampling: Emphasis on representative sampling (ISO 15528), cool/dark storage and immediate addition of dry acetonitrile after weighing due to isocyanate reactivity and toxicity.
Applications and users
ISO 6923:2023 is intended for:
- Quality control and release testing in paints, coatings and adhesive manufacturing.
- Contract testing and accredited analytical laboratories performing compliance testing for residual monomer diisocyanates.
- R&D and formulation development groups monitoring free isocyanate content during product development and stability studies.
- Regulatory and occupational safety assessments where accurate quantification of monomeric diisocyanates is required.
Practical benefits include reproducible, validated results suitable for interlaboratory comparability and regulatory reporting.
Related standards
- ISO 4618 - Paints and varnishes: vocabulary (terminology).
- ISO 15528 - Sampling of paints, varnishes and raw materials.
- Method validation and interlaboratory test references (FEICA) are cited in the standard’s introduction and Annex A.
Keywords: ISO 6923:2023, monomeric diisocyanate, HPLC‑UV, UHPLC, PNBPA derivatization, coatings testing, MDI, TDI, IPDI, HDI, paints and varnishes, analytical method.