Ethylene Glycol Residue Testing for Face Masks: Methods, Standards, and Compliance Requirements

Ethylene glycol residue testing is a critical chemical safety evaluation for face masks, verifying that residual monomers from polyester-based materials and sterilization-related hydrolysis products remain within safe exposure limits. This technical article explains the sources of ethylene glycol in masks, the sample types subject to testing, the analytical methods used by accredited third-party laboratories, and the regulatory framework governing residual solvents and monomers in respiratory protective equipment and medical masks.

Technical Overview

Ethylene glycol (EG, CAS 107-21-1) is a low-molecular-weight diol that may be present as a residual chemical in disposable face masks and respirators. Although masks are physical barriers rather than chemically active products, trace chemical residuals can migrate from mask materials to the skin, lips, and respiratory mucosa during prolonged wear, making residue control an essential element of mask chemical safety assessment.

There are three principal sources of ethylene glycol residues in mask products. First, the melt-blown polypropylene and spunbond layers of some masks incorporate polyester (PET) based components or binder fibers, and ethylene glycol is the primary diol monomer used in polyester polymerization, leaving trace residuals in the fiber. Second, ethylene glycol and its derivatives are used in some antistatic agents, humectants, and coating formulations applied to nonwoven fabrics during finishing. Third, masks sterilized with ethylene oxide (EO) may contain ethylene glycol as a hydrolysis degradation product, since residual EO reacts with moisture to form EG during and after sterilization.

From a toxicological perspective, ethylene glycol is classified as a substance with systemic toxicity following significant exposure, with the kidney as the primary target organ and the central nervous system as a secondary target. While the dermal and inhalation exposure levels associated with mask wear are typically far lower than toxic thresholds, regulatory risk assessment frameworks such as ISO 10993-17 (toxicological risk assessment of medical device constituents) require that extractable and residual chemical levels be quantified and justified. Residue testing therefore serves as the quantitative basis for demonstrating that ethylene glycol exposure from mask use remains within tolerable intake levels.

Testing Samples

Medical Masks and Respirators

Finished medical devices represent the primary sample category, including surgical masks conforming to YY 0469, medical protective masks conforming to GB 19083, and filtering facepiece respirators such as KN95 and N95 types. Because these products are intended for clinical and prolonged-wear applications, they attract the most stringent chemical residual requirements.

Daily Protective and Civilian Masks

Reusable and disposable civilian masks, including those conforming to GB/T 32610, are tested when manufacturers pursue voluntary certification, product liability verification, or market surveillance compliance. Fabric masks containing polyester blended layers are of particular interest due to the monomer origin of ethylene glycol.

Raw Materials and Components

Upstream testing covers melt-blown nonwoven fabric, spunbond polypropylene fabric, PET nose bridge strips, polyester ear loops, binder fibers, and finishing chemical formulations. Testing at the material stage allows manufacturers to identify contamination at the source before value is added in converting operations.

Post-Sterilization and Stability Samples

Masks sterilized by ethylene oxide are tested after the aeration period to characterize both EO and its EG hydrolysis product. Retained samples from real-time and accelerated aging studies are also evaluated to confirm that residue levels do not increase during shelf life through continued hydrolysis or material degradation.

Testing Items

The core testing parameter is the ethylene glycol residual content of the mask, typically expressed in milligrams per kilogram (mg/kg) or micrograms per gram (μg/g) of sample. Depending on the product scope and regulatory objective, testing programs may be structured as follows:

• Ethylene glycol residue determination in the complete mask article (all layers combined)
• Layer-by-layer profiling to localize the residue source, for example melt-blown filter media versus ear loops versus nose strip
• Companion residual testing for ethylene oxide (EO) and ethylene chlorohydrin (ECH) on EO-sterilized products, in accordance with the residual family approach of ISO 10993-7
• Extraction studies simulating prolonged skin contact and respiratory humidity exposure conditions
• Method validation parameters including linearity, detection limit, quantification limit, recovery, repeatability, and reproducibility

Testing Methods

Sample Preparation and Extraction

Representative mask specimens are cut into small pieces under controlled conditions to avoid cross-contamination. Extraction is generally performed with ultrapure water or a water-methanol system, using sealed vials with temperature-controlled incubation. Two extraction strategies are commonly applied: simulated-use extraction, in which the extraction conditions model the moisture, temperature, and contact duration of actual mask wearing, and exhaustive extraction, which recovers the total residual content for worst-case risk assessment purposes.

Chromatographic Analysis

The dominant analytical platform is gas chromatography with flame ionization detection (GC-FID), which offers robust quantification of ethylene glycol after suitable sample introduction. Where enhanced specificity and confirmation are required, gas chromatography coupled with mass spectrometry (GC-MS) is employed to verify analyte identity through retention time and characteristic ion ratios. Liquid chromatography with refractive index detection or evaporative light scattering detection may be used as an alternative technique for thermally demanding matrices. Calibration is performed using matrix-matched or standard-addition approaches to compensate for the nonwoven fiber matrix.

Quantification and Quality Control

Quantification relies on multi-point external calibration curves covering the expected residue range, with procedural blanks, duplicate determinations, and spiked recovery samples included in each analytical batch. Method performance is typically validated to achieve quantification limits well below the single-digit microgram-per-gram level, ensuring sensitivity adequate for the low residue levels expected in compliant mask products.

Evaluation Against Limits

Because ethylene glycol is evaluated primarily through risk-based tolerable intake derivation rather than a single universal numeric limit, accredited laboratories compare measured residue levels against thresholds derived from ISO 10993-17 methodology, product-specific national standards, or client-specified internal specifications. For EO-sterilized masks, the combined assessment of EO, ECH, and EG residuals against the framework of ISO 10993-7 provides an integrated demonstration of sterilization residue safety.

Applications

Ethylene glycol residue testing supports multiple compliance and quality objectives across the mask supply chain:

• Regulatory registration and technical file documentation for medical masks placed on national markets
• Verification of aeration efficiency and residue dissipation following ethylene oxide sterilization
• Incoming material control programs at mask converting facilities, targeting nonwoven fabrics and polyester components
• Support for biocompatibility evaluations under the ISO 10993 series, complementing cytotoxicity, irritation, and sensitization testing
• Export compliance dossiers where destination jurisdictions require documented chemical residual safety for personal protective equipment
• Root cause investigation of customer complaints, off-odor reports, or market surveillance failures
• Stability and shelf-life studies confirming that residue levels remain acceptable throughout the labeled product lifetime

FAQ

Why is ethylene glycol tested in masks even though masks are not ingested?

Ethylene glycol can migrate from mask materials to facial skin and lips, and trace vapor-phase transfer to the breathing zone is also evaluated in conservative exposure scenarios. Risk-based frameworks require quantification of such extractable residuals to demonstrate that cumulative exposure during realistic wear durations stays within tolerable intake levels.

What is the relationship between ethylene oxide sterilization and ethylene glycol residues?

Residual ethylene oxide reacts with water to form ethylene glycol. Masks sterilized with EO are therefore evaluated for the full residual family, including EO itself, ethylene chlorohydrin, and ethylene glycol, to ensure that post-sterilization aeration has adequately reduced all related species.

How much sample is required for testing?

A typical residue determination requires the equivalent of several complete masks or a comparable mass of cut fabric, generally on the order of a few grams of material, along with additional retained units for confirmatory or duplicate testing.

Which standards are relevant to this testing?

Relevant references include the ISO 10993 series for biological evaluation of medical devices, particularly ISO 10993-7 for sterilization residuals and ISO 10993-17 for toxicological risk assessment, together with product standards such as YY 0469, YY/T 0969, GB 19083, and GB/T 32610 for masks, and validated chromatographic method conventions consistent with ISO/IEC 17025 laboratory practice.

How should manufacturers respond if residue levels are elevated?

Corrective actions typically include sourcing alternative nonwoven or polyester materials with lower residual monomer content, optimizing finishing chemical formulations, extending post-sterilization aeration time or temperature, and re-validating the sterilization cycle, followed by retesting to confirm that residue levels have returned to specification.