Ethylene Glycol Migration and Residue Testing: Methods, Standards, and Regulatory Compliance

Ethylene glycol migration and residue testing verifies the safety of PET packaging, polyester coatings, and other food contact materials by quantifying residual monomer transfer into food and beverages. This technical guide covers regulatory limits, sample types, migration test conditions, GC-MS and HPLC analytical methods, and quality control workflows used by accredited testing laboratories. It is an essential reference for packaging manufacturers, brand owners, and regulatory affairs teams seeking compliance with EU, FDA, and Chinese national standards.

Technical Overview

Ethylene glycol (EG, CAS No. 107-21-1) is the primary diol monomer used in the production of polyethylene terephthalate (PET) and other polyesters through esterification or transesterification with terephthalic acid or dimethyl terephthalate. Because polymerization is never perfectly complete, a small fraction of free ethylene glycol remains in the finished resin. Additional free monomer can also be regenerated during melt processing, thermal degradation, hydrolysis, or mechanical recycling of PET. Under real-use conditions, this residual ethylene glycol can migrate from the packaging material into food, beverages, pharmaceuticals, or cosmetics, making reliable migration and residue testing a critical element of food contact safety compliance.

From a toxicological perspective, ethylene glycol is absorbed through the gastrointestinal tract and metabolized to glycolaldehyde, glycolic acid, and ultimately oxalic acid. The formation of calcium oxalate crystals is associated with renal injury and central nervous system effects, which is why regulatory authorities worldwide have established strict limits. Under European Union Regulation (EU) No 10/2011 on plastic materials intended to come into contact with food, ethylene glycol carries a specific migration limit (SML) of 30 mg/kg of food or food simulant. Chinese national standards, including GB 4806.6 for plastic resins and GB 4806.7 for plastic materials and articles, apply an aligned SML of 30 mg/kg. In the United States, PET resins are regulated under 21 CFR 177.1630, and manufacturers verify residual monomer content as part of their compliance programs.

It is important to distinguish between two related but different measurements. Migration testing determines how much ethylene glycol transfers from a material into a food simulant under controlled time and temperature conditions that simulate intended use. Residue testing determines the total amount of free ethylene glycol present within the material itself, typically obtained by solvent extraction. Both measurements are routinely performed together with diethylene glycol (DEG, CAS No. 111-46-6), a common co-product of PET synthesis that is also subject to a separate 30 mg/kg SML in the EU.

Testing Samples

PET Beverage Bottles, Preforms, and Closures

Rigid PET bottles for water, carbonated soft drinks, juices, tea, and edible oil represent the largest volume of samples submitted for ethylene glycol migration testing. Both finished bottles and injection-molded preforms can be evaluated, and testing is frequently extended to include closures, liners, and sealing gaskets.

PET Food Trays and OVENABLE Containers

Crystallized PET (CPET) trays used for ready meals, dual-ovenable containers, and microwaveable packaging require testing under elevated-temperature migration conditions, because thermal exposure accelerates monomer release and hydrolytic degradation of the polymer matrix.

Flexible Packaging and Laminates

PET films, metallized PET layers, and multilayer laminates used for snack bags, pouches, and sleeve labels are tested by immersion or in dedicated migration cells. The accessible food contact layer determines the migration behavior, so laminate construction details must be provided to the laboratory.

Polyester-Based Can Coatings and Coil Coatings

Polyester and polyester-melamine interior coatings on metal beverage cans, food cans, and drawn-and-rewall containers contain residual ethylene glycol from resin synthesis. These coatings are tested as coated panels or finished cans, with exposure conditions matched to hot-fill, retort, or pasteurization processes.

Pharmaceutical and Cosmetic Packaging

PET bottles for oral liquids, tablets, eyedrops, and personal care products are evaluated for ethylene glycol migration where product safety assessments or pharmacopoeial expectations require monomer control.

Polyester Fibers, Nonwovens, and Resins

Polyester staple fiber, filament yarns, spunbond nonwovens, and unsaturated or thermoplastic polyester resins may be tested for residual ethylene glycol content to support process control, incoming material qualification, and downstream compliance declarations.

Recycled PET (rPET) Flakes and Products

Mechanical and chemical recycling processes alter the residual monomer profile of PET. Recyclers and converters test rPET flakes, pellets, and converted articles to validate decontamination efficiency, support recycling process authorizations, and satisfy growing recycled-content requirements.

Testing Items

Accredited laboratories typically structure ethylene glycol testing around the following items:

• Specific migration of ethylene glycol into aqueous food simulants, including simulant A (10% ethanol), simulant B (3% acetic acid), simulant C (20% ethanol), and simulant D1 (50% ethanol).
• Specific migration into fatty food simulants, using olive oil or substitute simulants such as 95% ethanol or iso-octane where validated methods apply.
• Co-determination of diethylene glycol migration in the same analytical run.
• Total residual (free) ethylene glycol content in the material, determined by exhaustive solvent extraction.
• Migration testing under standardized time and temperature regimes, for example 10 days at 40 °C for long-term room-temperature storage, 2 hours at 70 °C for hot-fill applications, or 1 hour at 100 °C for boiling-water contact.
• Compliance assessment against the 30 mg/kg SML referenced in Regulation (EU) No 10/2011 and the corresponding Chinese national standards.

Testing Methods

Migration Test Procedure

Migration testing follows the general rules of GB 31604.1-2015 in China and Annex III to Regulation (EU) No 10/2011 in the EU. Articles that can be filled, such as bottles and trays, are filled with food simulant to the representative capacity. Flat materials, films, and coated panels are exposed by total immersion or in migration cells at a standard surface-to-volume ratio of 6 dm² per kilogram of food unless the actual ratio is known. Test specimens are held in temperature-controlled incubators for the selected duration, after which the food simulants are collected, cooled, and analyzed. Multiple migration steps may be applied to simulate repeated use articles.

Extraction for Residue Determination

For residual content testing, the sample is cut or milled to increase surface area and extracted with a suitable solvent, commonly water, methanol, or acetone, using reflux, ultrasonic extraction, or accelerated solvent extraction. The extract is then analyzed directly or after concentration and derivatization, and the result is expressed in mg/kg of material.

Instrumental Analysis by GC-MS and GC-FID

The reference approach for ethylene glycol in food simulants and extracts is gas chromatography coupled with flame ionization detection (GC-FID) or mass spectrometry (GC-MS), consistent with GB 31604.44-2016, the Chinese national standard for the determination of ethylene glycol and diethylene glycol migration in food contact materials and articles. Because ethylene glycol is highly polar, has low volatility, and exhibits strong adsorption on active sites, derivatization with BSTFA (N,O-bis(trimethylsilyl)trifluoroacetamide), often containing 1% TMCS, is widely used to convert ethylene glycol into its trimethylsilyl ether. Derivatization substantially improves chromatographic peak shape, volatility, and detection sensitivity. An internal standard such as 1,4-butanediol is typically added before sample preparation to correct for injection and derivatization variability.

Alternative HPLC and LC-MS Techniques

High performance liquid chromatography with refractive index detection (HPLC-RI) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) offer viable alternatives, particularly for aqueous simulants where direct injection is possible without derivatization. LC-MS/MS provides the highest selectivity for complex matrices and can achieve lower reporting limits than conventional RI detection.

Method Validation and Quality Control

Quantification is performed using matrix-matched external calibration covering the regulatory range. Typical performance indicators for validated methods include limits of quantification in the range of 0.5 to 1 mg/kg in aqueous simulants, recoveries between 80% and 110%, and repeatability precision within 10% relative standard deviation. Method validation follows the principles of ISO/IEC 17025 and GB/T 27404, and routine batches incorporate procedural blanks, duplicate determinations, and spike recovery controls.

Applications

• Regulatory compliance testing of new PET packaging for market access in the EU, the United States, China, and other jurisdictions.
• Batch release testing and periodic verification by PET resin producers, preform converters, and bottle manufacturers.
• Validation of mechanical and chemical PET recycling processes, including submissions supporting recycling process safety evaluations.
• Food contact substance notifications and customer-specific compliance declarations requiring monomer migration data.
• Shelf-life and accelerated aging studies that correlate storage duration and temperature with ethylene glycol release.
• Investigation of out-of-specification results, thermal process excursions, and supplier quality disputes.
• Research and development support for new polyester formulations, coatings, and barrier structures with reduced monomer content.

FAQ

What is the regulatory limit for ethylene glycol migration?

In the EU under Regulation (EU) No 10/2011 and in China under the GB 4806 series, the specific migration limit for ethylene glycol is 30 mg/kg of food or food simulant. Diethylene glycol is subject to a separate SML of the same value, which is why both analytes are usually measured together. In the United States, PET for food contact is governed by 21 CFR 177.1630, and residual monomer levels are verified as part of the manufacturer's compliance documentation.

Why are ethylene glycol and diethylene glycol tested together?

Diethylene glycol is formed as a side product during PET polymerization and can also arise from etherification of ethylene glycol during melt processing. Because both compounds share similar analytical behavior after silyl derivatization and are regulated with comparable limits, simultaneous determination in a single GC-MS or GC-FID run is efficient and cost-effective.

Which food simulants are used for ethylene glycol migration testing?

Aqueous simulants are the most relevant because ethylene glycol is fully miscible with water. Simulant A (10% ethanol) is used for aqueous foods, simulant B (3% acetic acid) for acidic foods, and simulant C (20% ethanol) or D1 (50% ethanol) for alcoholic and milk-like foods. Fatty food simulants such as olive oil or validated substitutes are applied when the article contacts oily foods, although ethylene glycol partitioning into lipids is comparatively low.

How is migration testing different from residue testing?

Migration testing measures the amount of ethylene glycol that actually transfers into a food simulant under realistic time and temperature conditions, which is what the SML legally controls. Residue testing measures the total free ethylene glycol contained in the material itself, obtained by exhaustive solvent extraction. Residue data are useful for process control and material qualification, while migration data are required for regulatory compliance.

What detection limits can be achieved?

With GC-MS following trimethylsilyl derivatization, validated methods commonly achieve limits of quantification of approximately 0.5 to 1 mg/kg in aqueous simulants, comfortably below the 30 mg/kg SML. Direct aqueous injection GC-FID methods typically report at slightly higher quantification levels but remain adequate for most compliance purposes.

How should samples be submitted for testing?

Laboratories generally require finished articles or representative material samples sufficient to provide at least 1 dm² of contact surface per test condition, along with information on intended use, contact food type, contact time, and maximum use temperature. Providing this information ensures that the correct simulant and migration conditions are selected and that results are defensible in regulatory submissions.

How long does ethylene glycol migration testing take?

For standard 10-day at 40 °C migration conditions, the exposure period alone accounts for ten working days, and instrumental analysis, derivatization, and reporting typically add several more days. Overall turnaround times of two to three weeks are common, while accelerated short-duration conditions can shorten the schedule when justified by the intended application.