Total Ethylene Glycol Residue Testing: Methods, Standards, and Applications

Total ethylene glycol (EG) residue testing quantifies residual ethylene glycol and related ethylene oxide sterilization byproducts in medical devices, pharmaceuticals, cosmetics, food contact materials, and industrial products. Using validated gas chromatography (GC-FID, GC-MS), headspace GC, and HPLC techniques, accredited laboratories deliver accurate, standards-compliant residue data for regulatory submission and quality control. This technical guide explains the principles, sample types, analytical methods, regulatory limits, and practical applications of total ethylene glycol residue determination.

Technical Overview

Ethylene glycol (EG, CAS No. 107-21-1) is a colorless, odorless, hygroscopic dihydric alcohol widely used in polyester production, antifreeze formulations, and industrial processes. In the medical device industry, ethylene glycol is primarily generated as a reaction byproduct during ethylene oxide (EO) sterilization: EO reacts with moisture present on device surfaces and in packaging to form ethylene glycol, and with chloride-containing materials to form ethylene chlorohydrin (ECH, 2-chloroethanol). These residues can remain adsorbed within polymers, adhesives, coatings, and cellulosic components after sterilization and may migrate to patients during clinical use.

Exposure to excessive ethylene glycol presents significant toxicological risks, including central nervous system depression, metabolic acidosis, and renal toxicity caused by oxalate crystal deposition. For EO-sterilized medical devices, residual EG is evaluated together with EO and ECH under the biological evaluation framework of ISO 10993-7 (identical to GB/T 16886.7 in China), which establishes tolerable exposure limits for EO and ECH and requires a risk-based toxicological assessment for EG in accordance with ISO 10993-17. "Total residue" testing therefore refers to the quantitative determination of all extractable ethylene glycol present on or within a product, expressed as mg per device, μg/g, or mg/day of patient exposure.

Because ethylene glycol is polar, poorly volatile (boiling point 197 °C), and lacks a strong UV chromophore, its accurate determination demands carefully validated chromatographic methods, controlled extraction conditions, and rigorous quality assurance. Third-party testing laboratories operating under ISO/IEC 17025 accreditation provide the traceable analytical data required for product registration, sterilization validation, and routine release testing.

Testing Samples

Ethylene Oxide–Sterilized Medical Devices

This is the largest category of samples submitted for total EG residue testing. Typical products include intravenous catheters, syringes, infusion and transfusion sets, hemodialyzers, blood oxygenators, wound dressings, surgical meshes, absorbable and non-absorbable sutures, breathing circuits, endotracheal tubes, drainage sets, and sterile packaging components made from polymers that are heat- or moisture-sensitive and therefore sterilized with EO gas.

Single-Use Infusion, Transfusion, and Injection Equipment

Devices in direct contact with circulating blood or infusion fluids are subject to stringent residual controls under product standards such as GB/T 14233.1, which specifies chromatographic procedures for determining ethylene oxide sterilization residues and related hydrolysis products in aqueous extracts of the device.

Cosmetics and Personal Care Products

Glycol-based humectants and solvents (propylene glycol, glycerin, butylene glycol) may contain monoethylene glycol as an impurity or adulterant. Total EG residue testing supports formulation safety assessments and compliance with regional cosmetic regulations and impurity specifications.

Food Contact Materials and PET Packaging

Residual ethylene glycol monomer in polyethylene terephthalate (PET) and recycled PET (rPET) materials, as well as migration into food simulants, is evaluated to verify compliance with food contact regulations such as EU Regulation (EU) No 10/2011 and FDA 21 CFR 177.1630.

Pharmaceutical Products, Excipients, and E-Liquids

Glycerin and propylene glycol excipients, oral and topical formulations, and electronic cigarette liquids are screened for ethylene glycol contamination, since substitution of lower-cost EG for pharmaceutical-grade glycols has historically caused serious poisoning incidents and remains a recognized global supply-chain risk.

Industrial Materials and Fluids

Polyester and polyurethane resins, polyester polyols, coolants, antifreeze concentrates, brake fluids, and hydraulic fluids are tested to verify ethylene glycol content, purity grades, and residual free-monomer levels for quality control and specification conformance.

Testing Items

Typical analytical scope for a total ethylene glycol residue testing program includes:

• Total residual ethylene glycol (EG) content, reported as mg/device, μg/g, μg/mL, or mg/day patient dose
• Residual ethylene oxide (EO) determination
• Residual ethylene chlorohydrin (ECH, 2-chloroethanol) determination
• Complete EO sterilization residual profile (EO + ECH + EG) within a single study
• Simulated-use extraction studies at physiological conditions (37 °C aqueous extraction)
• Exhaustive extraction studies to determine total residual burden
• Residual decline (aeration/degassing) curve studies for sterilization cycle optimization
• Method validation covering specificity, linearity, range, accuracy, precision, limit of detection (LOD), and limit of quantification (LOQ)
• Toxicological equivalence assessment of measured doses against ISO 10993-7 allowable limits and ISO 10993-17 derived limits

Testing Methods

Sample preparation is the critical first step. Solid devices are cut into representative sections, accurately weighed, and extracted using one of two strategies defined by ISO 10993-7: simulated-use extraction, which mimics clinically realistic product-fluid contact at 37 °C, or exhaustive extraction, in which repeated extractions continue until the residue recovered in a subsequent extraction falls below 10% of the first. Liquid samples are analyzed directly or after dilution and filtration. Salting-out additives may be employed to improve headspace partitioning of ethylene glycol.

The principal instrumental techniques include:

• Headspace gas chromatography with flame ionization detection (HS-GC-FID): the preferred routine method for volatile sterilization residuals, capable of quantifying EO, ECH, and EG from sealed-vial headspace injections with minimal matrix interference
• Direct-injection GC-FID using polar wall-coated open tubular (WAX-type) capillary columns for direct EG quantification in aqueous or methanolic extracts
• Derivatization GC (for example, silylation with BSTFA) followed by GC-FID or GC-MS to enhance volatility and detector response for trace-level EG
• GC-MS in selected ion monitoring mode for confirmatory identification and low-level quantification in complex matrices
• HPLC with refractive index (RI), charged aerosol (CAD), or evaporative light scattering (ELSD) detection as an orthogonal technique for non-volatile, highly polar matrices
• Ion chromatography for glycol determination in high-salt or ionic sample matrices

Quantification is performed using external or internal standard calibration (common internal standards include propylene glycol or isotopically labeled ethylene glycol) across a validated working range, typically from sub-microgram to milligram levels. Results are converted into per-device doses and compared with the allowable limits in ISO 10993-7 / GB/T 16886.7:

• Ethylene oxide (EO): 4 mg for limited exposure devices (≤24 h), 2 mg for prolonged exposure devices (24 h to 30 days), and 0.1 mg/day for permanent contact devices (>30 days)
• Ethylene chlorohydrin (ECH): 5 mg for limited exposure devices, 5 mg for prolonged exposure devices, and 2 mg/day for permanent contact devices
• Ethylene glycol (EG): evaluated case-by-case through toxicological risk assessment; because ISO 10993-7 does not assign a single numerical limit to EG, manufacturers commonly adopt internal acceptance criteria justified via ISO 10993-17 or product-specific standards

Quality assurance measures include matrix-matched calibration, spike recovery verification (typically 80–120%), replicate extraction precision (RSD ≤5–10%), procedural blanks, control charts, and participation in interlaboratory comparisons, all executed within an ISO/IEC 17025 management system to ensure data traceability and defensibility.

Applications

Total ethylene glycol residue testing supports a broad range of regulatory, quality, and development objectives:

• Regulatory submissions: technical documentation for NMPA device registration, FDA 510(k) and PMA premarket notifications, EU MDR CE marking, and submissions in other jurisdictions requiring sterilization residual data
• Sterilization validation: residual measurements during EO cycle development, half-cycle and full-cycle validation studies, and performance qualification of aeration parameters
• Routine batch release: periodic or lot-by-lot verification that sterilization residues remain within established limits
• Aeration optimization: residual decline curves that allow manufacturers to shorten degassing time while maintaining compliance, reducing inventory holding costs
• Materials and supplier qualification: comparison of polymer grades, adhesives, and packaging configurations for residual adsorption and desorption behavior
• Shelf-life and stability studies: confirmation that residues do not increase or leach disproportionately over the claimed expiry period
• Failure analysis and complaint investigation: root-cause determination for out-of-specification results or reported adverse events
• Consumer and industrial product safety: impurity screening of glycerin, propylene glycol, e-liquids, cosmetics, coolants, and PET materials

FAQ

Q: Why does ethylene glycol residue appear on EO-sterilized products?

A: During ethylene oxide sterilization, EO gas reacts with water molecules on device surfaces and inside polymer matrices. This hydrolysis reaction converts EO into ethylene glycol, which is less volatile than EO and can therefore persist within the product for extended periods unless adequate aeration is applied after the sterilization cycle.

Q: What sample quantities are required for testing?

A: Typical submission requirements are 3 to 10 complete sterile devices per test condition for medical devices, 10 to 50 mL for liquid samples, and 5 to 20 g for polymeric or granular materials. Exhaustive extraction studies and method validation generally require additional sample units. Samples should remain in their original sterile packaging and be shipped under conditions that prevent additional moisture uptake or residue loss.

Q: How are results reported and evaluated?

A: Ethylene glycol residues are reported in mass units (mg/device or μg/g) and, where clinically relevant, converted to an average daily patient dose for comparison against allowable limits. A comprehensive report includes the extraction method, chromatographic conditions, calibration data, quality control results, and a pass/fail conclusion against the applicable standard.

Q: What is a typical turnaround time?

A: Routine single-point residue testing is generally completed within 5 to 10 working days after sample receipt. Exhaustive extraction studies, full sterilization residual profiles, and method validation projects may require two to four weeks depending on the extraction protocol and matrix complexity.

Q: Can EO, ECH, and EG be measured in one analysis?

A: Yes. Modern HS-GC-FID and GC-MS methods can separate and quantify ethylene oxide, ethylene chlorohydrin, and ethylene glycol in a single chromatographic run from the same extract, providing an efficient and internally consistent total sterilization residual profile.

Q: How can manufacturers reduce ethylene glycol residues?

A: Effective mitigation strategies include optimizing EO sterilization cycle parameters (gas concentration, humidity, temperature, and exposure time), extending or heating aeration phases, selecting lower-absorbing packaging films, increasing packaging permeability to EO and moisture, and allowing adequate post-sterilization quarantine time verified through residual decline testing.