Ethylene Glycol Residue Testing in Solid Samples: Methods, Standards, and Applications

Ethylene glycol residue testing in solid samples is a critical safety and quality control analysis widely performed across the pharmaceutical, food packaging, polymer, textile, and cosmetics industries. Using validated chromatographic techniques such as GC-FID, GC-MS, and HPLC, accredited third-party laboratories can accurately quantify trace-level ethylene glycol in complex solid matrices to demonstrate regulatory compliance and protect consumer safety. This article provides a comprehensive overview of the testing scope, sample types, analytical methods, validation criteria, and practical considerations involved in ethylene glycol residual determination.

Technical Overview

Ethylene glycol (EG, CAS No. 107-21-1) is a colorless, odorless, hygroscopic dihydric alcohol with the molecular formula C2H6O2 and a molecular weight of 62.07 g/mol. It is fully miscible with water and lower alcohols and is one of the most widely produced industrial chemicals, used in antifreeze and coolant formulations, as a monomer in polyethylene terephthalate (PET) and polyester production, as an intermediate in polyurethane synthesis, and as a humectant, plasticizer, and chemical feedstock.

Although ethylene glycol has relatively low acute oral toxicity compared with some industrial solvents, it is metabolized in the human body via alcohol dehydrogenase to glycolaldehyde, glycolic acid, and oxalic acid, causing metabolic acidosis, central nervous system depression, and severe renal injury. Chronic exposure to residual levels is also of toxicological concern. For this reason, residual ethylene glycol in finished solid products must be strictly controlled.

In solid matrices, ethylene glycol residues typically originate from incomplete polymerization or insufficient drying of PET and polyurethane materials, impurities or degradation of polyethylene glycol (PEG)-based excipients, migration from food contact packaging, textile finishing and anti-static treatments, and process carryover in chemical synthesis. Relevant regulatory references include the specific migration limit of 30 mg/kg food for ethylene glycol established in the European plastics regulation (EU) No 10/2011, pharmacopoeial limit tests for ethylene glycol and diethylene glycol in glycerin-, sorbitol-, and PEG-containing materials under USP and Ph. Eur. monographs, and national food contact material standards such as the GB 31604 series. Analytically, ethylene glycol presents a challenge because of its high polarity, low volatility, and absence of a strong chromophore, which makes careful method selection and derivatization strategies essential.

Testing Samples

Pharmaceutical Products and Excipients

Solid oral dosage forms, active pharmaceutical ingredients, lyophilized powders, capsule shells, and granular excipients such as polyethylene glycols, sorbitol, and glycerin-derived materials are tested to verify compliance with pharmacopoeial limits for ethylene glycol and diethylene glycol, following the principles of ICH quality guidelines and USP or Ph. Eur. monograph requirements.

Food Contact Materials and Packaging

PET bottle preforms and containers, plastic films, laminates, inner liners, coatings, adhesives, and can lacquers are analyzed for residual ethylene glycol and for migration behavior into food simulants, in accordance with (EU) No 10/2011 and the GB 31604 series of national food safety standards.

Polymers, Resins, and Plastics

PET resin chips, polyester fibers, polyurethane foams, thermoplastic polyurethane (TPU), alkyd resins, and unsaturated polyester formulations are tested to quantify residual monomer content, evaluate polymerization completeness, and support process optimization and incoming material inspection.

Textiles and Consumer Products

Fabric rolls, nonwoven wipes, hygiene products, and finished textile goods that have been treated with finishing, anti-freeze, humectant, or anti-static agents may carry ethylene glycol residues and are screened prior to shipment or certification.

Cosmetics and Personal Care Products

Pressed powders, dry sheet masks, solid sticks, soap bases, and granular formulation components are tested as part of raw material qualification and finished product safety assessment under applicable cosmetic regulatory frameworks.

Industrial and Specialty Solids

Granular chemicals, adsorbents, catalyst supports, filter media, dessicant-adjacent materials, tobacco products, and solid agrochemical formulations are analyzed for ethylene glycol carryover arising from synthesis, coating, or conditioning steps.

Testing Items

The core analytical target is the quantitative determination of residual ethylene glycol in the solid matrix, reported in mg/kg (ppm), mg/g, or percentage by weight depending on the expected concentration range. Related glycols are frequently determined simultaneously in a single chromatographic run:

• Ethylene glycol (EG, CAS 107-21-1) — primary target analyte
• Diethylene glycol (DEG, CAS 111-46-6) — common co-impurity and toxicological marker
• Triethylene glycol (TEG, CAS 112-27-6) — oligomeric impurity in PET and PEG systems
• Propylene glycol (PG, CAS 57-55-6) — companion humectant and coolant residue
• 1,4-Butanediol and higher glycols — optional extended screening
• Total glycol content — sum parameter for polymer and process evaluation

Typical limits of quantification reach 1 to 10 mg/kg for GC-MS-based methods with derivatization and 10 to 50 mg/kg for direct HPLC-refractive index approaches, which is sufficient to demonstrate compliance with most regulatory and contractual thresholds.

Testing Methods

Sample Preparation and Extraction

Solid samples are homogenized by cutting, milling, or cryogenic grinding to reduce particle size and improve extraction efficiency. Ethylene glycol is then extracted using water, methanol, or aqueous-alcoholic mixtures by ultrasonic extraction, shaking, accelerated solvent extraction, or reflux. An internal standard such as 1,3-propanediol or 1,4-butanediol is added at the beginning of extraction to correct for volumetric and matrix-related variations. For migration studies, specimens are immersed in food simulants under defined time and temperature conditions before analysis of the simulant.

Gas Chromatography with Flame Ionization Detection (GC-FID)

GC-FID is the workhorse technique for glycol quantification. Direct aqueous injection onto a polar polyethylene-glycol-based wax capillary column provides adequate resolution for routine quality control at moderate concentration levels, while general methodological guidance can be drawn from ASTM E202 for the analysis of glycols. Quantification is performed against multi-point calibration curves using an internal standard.

Derivatization Followed by GC or GC-MS

Because ethylene glycol is highly polar and only moderately volatile, silylation with reagents such as BSTFA with TMCS converts the analyte into its volatile bis-trimethylsilyl ether derivative, dramatically improving peak shape, chromatographic focus, and sensitivity. The derivatized extract is then analyzed by GC-FID or, for maximum selectivity and lower detection limits, by GC-MS in selected ion monitoring mode, which effectively eliminates matrix interferences from complex solids such as polymers and biological matrices.

Headspace Gas Chromatography

Static or dynamic headspace sampling with elevated incubation temperatures can be applied to thermally stable matrices where cleaner chromatograms are required, offering a fully automated and solvent-minimized workflow when the residual levels are sufficiently high.

High Performance Liquid Chromatography (HPLC)

HPLC with refractive index detection or evaporative light scattering detection on amino, carbohydrate, or ion-exclusion columns provides a non-derivatization alternative that is particularly suitable for thermally labile matrices and for the simultaneous separation of EG, DEG, TEG, and PG in a single isocratic run.

Method Validation and Quality Assurance

All procedures are validated and executed under an ISO/IEC 17025-aligned quality system covering specificity, linearity (typically R² greater than 0.995), accuracy (spike recovery of 85 to 110 percent), precision (RSD below 5 percent for replicate preparations), limits of detection and quantification, robustness, and measurement uncertainty. Each analytical batch includes reagent blanks, matrix spikes, duplicate preparations, and continuing calibration verification to guarantee defensible results.

Applications

Ethylene glycol residue testing in solid samples supports a broad range of quality, regulatory, and investigative objectives:

• Batch release testing and incoming material inspection for PET resins, polyurethane products, and pharmaceutical excipients
• Compliance demonstration against specific migration limits for food contact plastics under (EU) No 10/2011 and GB 31604 requirements
• Pharmacopoeial limit testing for ethylene glycol and diethylene glycol in glycerin-, sorbitol-, and PEG-containing products
• Extractables and leachables studies for packaging systems and medical devices
• Root cause investigation of contamination incidents, discoloration, odor, or process excursions
• Supplier qualification, material comparison, and technical due diligence in procurement
• Polymerization and drying process optimization, residual monomer trending, and stability or shelf-life studies
• Research and development support for new formulations, coatings, and bio-based materials

FAQ

What sample quantity is required for testing?

A minimum of 10 to 50 grams of homogenized solid material is generally sufficient, including allowance for duplicate preparations and confirmatory testing. For high-value or limited-availability samples, micro-extraction protocols requiring less than 1 gram can be validated on request.

What detection limits can be achieved?

With derivatization and GC-MS detection, limits of quantification of approximately 1 to 5 mg/kg are routinely attainable. Direct HPLC-refractive index methods typically achieve quantification limits of 10 to 50 mg/kg, which remains adequate for most industrial and food contact thresholds.

Can ethylene glycol and diethylene glycol be determined in the same analysis?

Yes. GC and HPLC methods are routinely optimized to separate and quantify EG, DEG, TEG, and propylene glycol simultaneously, which is more efficient and more informative than single-analyte testing, particularly for pharmaceutical and packaging investigations.

Why is derivatization sometimes necessary?

Ethylene glycol is highly polar and tends to adsorb on active sites in injection ports and columns, producing broad or tailing peaks. Silylation masks the hydroxyl groups, converts the analyte into a volatile derivative, and substantially improves sensitivity, reproducibility, and chromatographic selectivity.

How is cross-contamination prevented during analysis?

Laboratories use dedicated glassware baked at high temperature, avoid PEG-based labware and lubricants, run procedural blanks in every batch, and confirm findings with matrix spikes and mass-spectrometric identification to ensure reported residues genuinely originate from the sample.

What is the typical turnaround time?

Standard projects are completed within five to ten working days from sample receipt, depending on matrix complexity, extraction requirements, and whether additional confirmatory or migration testing is included. Rush services can often be arranged with accredited third-party laboratories for time-critical investigations.

Which reporting basis is used for the results?

Results are reported as milligrams of ethylene glycol per kilogram of sample (mg/kg, equivalent to ppm) or as a percentage by weight, calculated on either an as-received or dry-weight basis according to the client specification, and accompanied by full method information, calibration data, and measurement uncertainty where required.