Ethylene Glycol Residue Testing for Medical Devices: Standards, Methods, and Compliance Guidance

Ethylene glycol (EG) residue testing is a critical quality and safety requirement for medical devices sterilized with ethylene oxide (EO), verifying that sterilization byproducts remain within biologically safe limits defined by ISO 10993-7 and its Chinese adoption GB/T 16886.7. This technical article explains the sources and health significance of EG residuals, validated analytical methods such as GC, HPLC, and ion chromatography, and practical guidance on sample preparation, result evaluation, and regulatory compliance for medical device manufacturers.

Technical Overview

Ethylene glycol (EG, ethane-1,2-diol) is a polar, non-volatile compound that can remain in medical devices after ethylene oxide sterilization. During the sterilization cycle, residual EO reacts with moisture present in the product, packaging, or the sterilization chamber and hydrolyzes to form EG; the related byproduct ethylene chlorohydrin (ECH, 2-chloroethanol) can also degrade to EG over time. Unlike EO, which dissipates during forced-air aeration, EG has negligible volatility and high water solubility, so it tends to persist in hydrophilic materials such as cellulose-based dressings, natural rubber latex, polyurethane, and plasticized PVC, and it can leach into fluids delivered to the patient.

From a toxicological perspective, absorbed EG is metabolized to glycolate and oxalate, which can cause metabolic acidosis, central nervous system depression, and renal tubular injury associated with calcium oxalate deposition. For this reason, regulatory authorities and accredited third-party laboratories treat EG as a sterilization-related residue of concern that must be quantified and controlled whenever its formation is expected, particularly for devices with fluid paths or aqueous-contacting components.

Standards and Regulatory Framework

• ISO 10993-7 (Biological evaluation of medical devices — Part 7: Ethylene oxide sterilization residuals), adopted in Europe as EN ISO 10993-7 and in China as GB/T 16886.7, is the primary standard. It classifies device exposure as limited (up to 24 h), prolonged (24 h to 30 d), and permanent (over 30 d) and sets device-level tolerable exposure limits, for example 4 mg for EO and 9 mg for ECH per device for limited-contact use in an average 70 kg adult, with stricter limits for prolonged and permanent contact. Where EG formation is anticipated, the standard requires its evaluation alongside EO and ECH.
• ISO 11135 and GB 18279.1 govern validation and routine control of the EO sterilization process, including aeration parameters that directly influence residual levels.
• ISO 10993-12 specifies sample preparation and extraction procedures used for residual testing.
• ISO 10993-17 and ISO 10993-18 support the establishment of allowable limits and overall chemical characterization of leachables.
• Testing is typically performed by laboratories accredited to ISO/IEC 17025 to ensure method validity and data acceptability for regulatory submissions.

Testing Samples

Fully Processed, Sterilized Devices

The preferred test article is the finished device in its primary packaging, tested after completion of the validated aeration cycle, because this condition represents the product actually delivered to clinical use. Complete functional units are extracted in their entirety whenever feasible.

Fluid-Path and Aqueous-Contacting Devices

Intravenous infusion and transfusion sets, hemodialyzers, blood oxygenators, cardiotomy reservoirs, and solution containers carry the highest EG relevance, because any extractable glycol can be infused directly into the circulation. These devices are prioritized in residual monitoring programs.

Hydrophilic and Absorbent Materials

Wound dressings, absorbent pads, cellulose components, latex items, polyurethane catheters, and plasticized PVC tubing retain moisture during sterilization and therefore generate and retain more EG than hydrophobic polymers such as polyolefins or fluoropolymers.

Development, Supplier, and Stability Samples

Prototype builds, candidate materials, and supplier qualification lots are tested during design verification, while aged samples from real-time and accelerated shelf-life studies are tested to confirm that residual levels remain acceptable throughout the labeled expiry.

Testing Items

A comprehensive residuals evaluation for EO-sterilized devices typically includes the following items, reported both as concentration (micrograms per gram of device) and as delivered dose (milligrams per device):

• Ethylene glycol (EG) residue content
• Ethylene oxide (EO) residue content
• Ethylene chlorohydrin (ECH) residue content
• Total sterilization residuals relative to the tolerable exposure limits of ISO 10993-7 / GB/T 16886.7
• Simulated-use and exhaustive extraction studies to determine the worst-case patient dose
• Aeration or degassing efficiency verification supporting sterilization validation

Testing Methods

The analytical workflow consists of a defined sampling plan, extraction of the residue from the device, instrumental quantification, and evaluation of the calculated patient dose against the applicable allowable limits.

Sample Preparation and Extraction

Following ISO 10993-12 and the extraction guidance of ISO 10993-7, laboratories commonly use simulated-use extraction, in which the device is extracted in water or a simulated clinical fluid at physiological temperature for a duration reflecting actual clinical contact, and exhaustive extraction, in which repeated extractions continue until the residual quantity in a subsequent extract is negligible. Aqueous media are ideal for EG because of its complete miscibility with water.

Chromatographic Analysis of EG

• Gas chromatography with flame ionization or mass spectrometric detection (GC-FID, GC-MS) after derivatization, such as silylation, which converts EG into volatile derivatives suitable for GC determination.
• Direct aqueous injection GC on polar (polyethylene glycol phase) capillary columns, a simple approach suited to higher residue levels.
• High-performance liquid chromatography with refractive index or evaporative light-scattering detection (HPLC-RI, HPLC-ELSD), a robust solution for underivatized EG in aqueous extracts.
• Ion chromatography with pulsed amperometric detection, which offers high sensitivity and selectivity without derivatization.
• Liquid chromatography tandem mass spectrometry (LC-MS/MS) for trace-level quantification and confirmation.

Headspace GC, the standard technique for EO and ECH, is not suitable for EG because of its low vapor pressure, which is why liquid-based or derivatized methods are essential for reliable EG data.

Method Validation and Data Reporting

Validated methods document linearity, limits of detection and quantification, recovery, precision, and specificity in the relevant extract matrix. Results are converted to a per-device dose, compared with the tolerable exposure for the intended contact duration, and adjusted where necessary for small-body-weight or pediatric populations as allowed by the standard. A conformity statement against ISO 10993-7 / GB/T 16886.7 completes the test report.

Applications

• Validation and routine release testing for ethylene oxide sterilization processes, including aeration cycle confirmation
• Regulatory submissions for device registration in China, the United States, the European Union, and other jurisdictions that require sterilization residual data
• Design changes, material substitutions, and packaging modifications that may alter residual uptake or release
• Shelf-life and aging studies confirming residual stability through product expiry
• Root-cause investigations of out-of-specification residuals or adverse-event follow-up
• Supplier qualification and incoming material control for outsourced sterilization or components

FAQ

Why is EG tested if ethylene oxide was the sterilant?

EG is a hydrolysis product of EO and is formed whenever moisture is present during or after sterilization. Because EG is non-volatile, it does not off-gas during aeration and can accumulate in the device, so it must be measured independently of EO.

What is the best analytical technique for EG residues?

Ion chromatography with pulsed amperometric detection and HPLC with refractive index detection are widely used for aqueous extracts. GC-based determination is also accurate when EG is first converted to a volatile derivative by silylation.

When should samples be collected after sterilization?

Release testing is performed after the full validated aeration and hold time has elapsed, so that results represent the worst case delivered to the patient. Additional time points during stability studies confirm that levels remain within limits through expiry.

How are the results judged as pass or fail?

The calculated delivered dose in milligrams per device is compared with the tolerable exposure limits for the applicable contact-duration category in ISO 10993-7 or GB/T 16886.7, with risk-based adjustment for patient population and device usage.

How many devices are needed for testing?

Requirements vary with device size and construction, but testing typically requires several complete sterile units to cover both simulated-use and exhaustive extraction, plus retained units in case of repeat analysis.