Determination of Ethylene Glycol Residue in Medical Devices: Standards, Methods, and Applications

Ethylene glycol (EG) residues in medical devices originate mainly from ethylene oxide sterilization by-products and from polymer manufacturing processes, making accurate quantification an essential part of chemical safety and biocompatibility evaluation. This article explains the regulatory framework, typical sample types, analytical techniques such as headspace gas chromatography and HPLC, and practical considerations for EG residue testing of medical devices in accredited third-party laboratories.

Residual ethylene glycol is a frequently evaluated chemical indicator for medical devices that are sterilized with ethylene oxide or manufactured from glycol-based polymers. Reliable determination of EG residue supports sterilization validation, batch release, and toxicological risk assessment throughout the product lifecycle.

Technical Overview

Ethylene glycol (EG; ethane-1,2-diol; CAS 107-21-1) is a highly polar, hydrophilic diol with a high boiling point of approximately 197 °C. In medical devices, EG residues arise from three principal sources: hydrolysis of ethylene oxide (EO) in the presence of moisture during humidified EO sterilization; residual monomers or reactants from the synthesis of polyethylene terephthalate (PET), polyurethanes, polyester adhesives, and coatings; and residual processing solvents used in component fabrication. Because EG is considerably less volatile and more persistent than EO, it can remain in device materials long after aeration and serves as a useful indicator of moisture exposure and degassing efficiency.

From a toxicological perspective, absorbed EG is metabolized to glycoaldehyde, glycolic acid, and oxalic acid, and elevated exposure is associated with central nervous system depression and renal injury caused by calcium oxalate deposition. Although EG is generally regarded as less hazardous than EO at equivalent doses, residue levels must still be characterized and controlled for devices with patient contact.

• ISO 10993-7 (and its Chinese counterpart GB/T 16886.7) defines the framework for evaluating ethylene oxide sterilization residuals, primarily EO and ethylene chlorohydrin (ECH), with contact-duration categories of limited (≤24 h), prolonged (24 h to 30 d), and enduring (>30 d) exposure.
• EG is commonly quantified alongside EO and ECH to complete the sterilization residue profile, and specific acceptance criteria are typically defined in product standards or derived from toxicological risk assessment.
• ISO 10993-12 governs sample preparation and extraction conditions, ISO 10993-18 addresses chemical characterization of extractables, and ISO 10993-17 provides the methodology for establishing allowable limits.
• GB/T 14233.1 specifies general chemical analysis methods, including chromatographic determination of sterilization residues, for infusion, transfusion, and injection equipment.

Testing Samples

EO-Sterilized Single-Use Devices

Syringes, infusion and transfusion sets, intravenous catheters, urethral and endotracheal catheters, hemodialyzers, oxygenators, wound dressings, surgical meshes, and tubings are frequently sterilized with ethylene oxide. These polymer-rich, moisture-absorbing devices represent the largest category of samples submitted for EG residue determination, since EO readily hydrolyzes to EG during the humidified sterilization phase.

Polymeric Materials and Components

PET films and containers, polyurethane potting compounds and tubings, polyester-based adhesives, coatings, laminates, and tapes may retain EG from polymerization or formulation processes. Resin granules, masterbatches, and finished components are tested during incoming material qualification and supplier evaluation programs.

Container-Closure and Packaging Systems

Primary packaging that directly contacts the device or a delivered fluid, such as PET bottles, blister trays, and multilayer laminates, can contribute EG to the contacting medium and is evaluated within extractables and leachables studies.

Process Validation and Stability Samples

Devices sampled at defined points across sterilization and aeration cycles, together with real-time and accelerated aging time points from shelf-life studies, are analyzed to demonstrate that EG residues are controlled at release and remain acceptable throughout the labeled expiry.

Testing Items

• EG residue content in the device extract, expressed as concentration (mg/L or µg/mL) and converted to total residue per device (mg/device) or per unit mass (µg/g).
• Co-determination of EO and ECH residues to provide a complete sterilization residual profile consistent with ISO 10993-7 and GB/T 16886.7.
• Screening for related glycols, such as diethylene glycol, where the material system indicates their possible presence.
• Method validation attributes, including specificity, linearity, limits of detection and quantification, recovery, and precision, reported per study requirements.
• Comparison of measured residue levels against product-specific limits or tolerable exposure values derived using ISO 10993-17 principles.

Testing Methods

Sample preparation follows ISO 10993-12 and ISO 10993-7 concepts. Simulated-use extraction, typically performed with water or an aqueous medium at 37 °C for 24 h to 72 h, estimates the clinically available residue fraction, while exhaustive extraction with justified solvents and elevated temperatures estimates the total residual burden. Extracts are prepared in sealed vessels to prevent cross-contamination and are analyzed promptly; unlike EO, EG is chemically stable in aqueous extracts, which simplifies handling and storage.

• Headspace gas chromatography with flame ionization detection (HS-GC-FID) provides rapid screening and enables co-analysis of volatile EO and ECH, although the low volatility of EG limits sensitivity and usually requires elevated equilibration temperatures.
• Direct-injection GC-FID or GC-MS of aqueous extracts, or analysis after derivatization such as silylation or benzoylation, substantially improves EG volatility, peak shape, and detectability, with mass spectrometric detection providing confident confirmation.
• High-performance liquid chromatography with refractive index detection (HPLC-RID) or evaporative light-scattering detection (HPLC-ELSD) is a robust solution for non-volatile, non-chromophoric EG, using isocratic separation and external calibration.
• LC-MS/MS methods achieve trace-level quantification and confirmation where very low reporting limits are required.
• Classical periodate oxidation followed by colorimetric detection of the generated formaldehyde remains available as a screening technique when chromatographic instrumentation is not required.

Quantification is performed with matrix-matched or external calibration, often using an internal standard such as 1,3-propanediol or 1,4-butanediol to correct for injection variability. Typical validation acceptance criteria include calibration linearity with a coefficient of determination of at least 0.995, spiked recovery between 80 % and 120 %, and replicate precision with a relative standard deviation not exceeding 10 %. Reported results are compared against tolerable exposure limits or product-standard requirements to establish conformity.

Applications

• Validation and requalification of ethylene oxide sterilization and aeration cycles, using EG data to optimize degassing time and temperature.
• Routine batch release testing and periodic control of EO-sterilized single-use devices.
• Regulatory dossier support for market approval submissions, demonstrating compliance with ISO 10993-7 and GB/T 16886.7 requirements.
• Raw material qualification, supplier control, and evaluation of design or material changes for PET-, polyurethane-, and polyester-based components.
• Extractables and leachables studies and chemical characterization per ISO 10993-18 within overall biological safety evaluations.
• Shelf-life and stability programs verifying that residue levels remain acceptable through the labeled expiry date.
• Investigation of out-of-specification results, customer complaints, and adverse event reports within ISO 14971 risk management processes.

FAQ

Q: Why is ethylene glycol tested if ISO 10993-7 sets numerical limits mainly for EO and ECH? A: EG is generated together with EO residues through hydrolysis and provides complementary evidence of moisture exposure and aeration efficiency. Many product-specific standards, customers, and toxicological assessments require EG data to complete the residue profile, even where harmonized EG limits are not explicitly defined.

Q: What extraction conditions are typically used? A: Simulated-use extraction with water at 37 °C for 24 h to 72 h is most common, reflecting the residue available to the patient. Exhaustive extraction is applied when the total residual content must be estimated, for example during process validation or material characterization.

Q: What detection limits can be achieved? A: Indicatively, HPLC-RID methods quantify EG at levels of several µg/mL, while derivatization GC-MS and LC-MS/MS approaches can reach sub-µg/mL reporting limits. Actual figures depend on the matrix and the validated method.

Q: Can EG, EO, and ECH be determined from the same sample? A: Yes. A common strategy analyzes the volatile EO and ECH by headspace GC and determines EG in the retained aqueous extract by direct-injection or derivatized GC, HPLC, or LC-MS, providing a complete residual profile from one extraction.

Q: How should results be judged? A: Results expressed as mg per device are compared with product-standard limits or with tolerable exposure values derived from the ISO 10993-17 methodology, taking into account the contact duration category of the device.

Q: How long does testing take? A: Routine EG determination in accredited third-party laboratories is generally completed within five to ten working days after sample receipt, while full method validation or multi-time-point sterilization studies may require several weeks.