Overview
ISO 2561:2023 - "Plastics - Determination of residual styrene monomer in polystyrene (PS) and impact‑resistant polystyrene (PS‑I) by gas chromatography" - specifies a validated laboratory method to quantify residual styrene monomer in PS and PS‑I using gas chromatography (GC). The method also supports simultaneous determination of other volatile aromatic hydrocarbons (for example, ethylbenzene, cumene, α‑methylstyrene). The fourth edition adds headspace injection (option C) as a formal sample‑introducing technique.
Key topics and technical requirements
- Principle: Dissolve polymer in solvent containing an internal standard; analyze styrene and other volatiles by GC.
- Sample introducing options:
- Option A: Direct injection of polymer solution.
- Option B: Inject supernatant after polymer precipitation.
- Option C: Headspace sampling (vial thermostated, vapor injected).
- Reagents & materials:
- Recommended internal standards: n‑butylbenzene, cyclopentanol, 1,2,4‑trimethylbenzene, 1,4‑diethylbenzene.
- Solvents: dimethylformamide (DMF), butanone, dichloromethane, tetrahydrofuran (THF - only for Option A). Option C uses DMF.
- Precipitators: 2,2,4‑trimethylpentane or ethanol.
- Aromatic standards: styrene and other target hydrocarbons; styrene must be checked for self‑polymerization.
- Apparatus & detectors:
- GC with appropriate column (packed or capillary; capillary preferred), suitable detector (FID commonly used), headspace sampler for Option C, syringes (1–50 µL), accurate analytical balance (0.1 mg), volumetric flasks, headspace vials.
- Carrier gases: hydrogen, helium or nitrogen (detector dependent); hydrogen and air for flame detectors (observe hydrogen safety).
- Procedural controls:
- Keep dilution temperatures