A diethylene glycol (DEG) residue assessment report provides documented, quantitative evidence of DEG levels in PET packaging, pharmaceutical excipients, cosmetics, and consumer products against pharmacopeial and food-contact regulatory limits. This technical guide explains the testing scope, analytical techniques such as GC-FID, GC-MS, and HPLC, the applicable standards including EU No 10/2011, GB 9685, and USP monographs, and how test results are interpreted for compliance certification.
Technical Overview
Diethylene glycol (DEG; CAS No. 111-46-6; molecular formula C4H10O3; molecular weight 106.12 g/mol) is a colorless, hygroscopic, water-miscible liquid produced as a by-product of ethylene glycol manufacture and ethylene oxide hydration. In the polymer industry, DEG is deliberately incorporated as a co-monomer in polyethylene terephthalate (PET), typically at 1–3% by weight, to regulate crystallization behavior and processability. In pharmaceuticals, cosmetics, and food applications, however, DEG is regarded as a hazardous impurity: it is metabolized in the body to toxic intermediates and oxalate, causing acute kidney injury, hepatotoxicity, and central nervous system depression. Historical mass-poisoning incidents involving DEG-contaminated glycerin and propylene glycol supplies have made residual DEG control a global regulatory priority.
A DEG residue assessment report is a structured technical document issued by an accredited third-party laboratory that identifies and quantifies residual DEG in a sample matrix, evaluates its migration potential where applicable, compares the measured values against statutory or pharmacopeial limits, and states an unambiguous conformity conclusion. A complete report typically includes sample identification and chain-of-custody information, a description of the analytical method and its validation parameters (calibration, recovery, repeatability), limits of detection (LOD) and quantification (LOQ), numerical results with measurement uncertainty, and a pass/fail determination against the applicable acceptance criteria.
Testing Samples
Polymer and Food Contact Materials
Samples include PET granules (virgin and recycled), preforms, blow-molded bottles, thermoformed trays and containers, polyester films and sheets, monofilaments, and polyester-based coatings, inks, and adhesives intended for direct food contact. Both the total DEG content of the polymer and the DEG migrating into food simulants can be assessed.
Pharmaceutical Excipients and Formulations
Matrices include glycerin (glycerol), propylene glycol, sorbitol solutions, polyethylene glycol grades, oral solutions, syrups, elixirs, suspensions, and topical formulations where glycerin-based excipients are used as diluents, humectants, or sweetening vehicles.
Cosmetics and Personal Care Products
Toothpaste, mouthwash, hand creams, lotions, glycerin soaps, and other leave-on or rinse-off products are screened, since contaminated glycerin supplies have historically entered cosmetic supply chains.
E-Liquids and Other Consumer Matrices
Electronic cigarette refill liquids containing glycerin and propylene glycol are assessed against pharmacopeial impurity limits, together with household chemicals and novel consumer formulations.
Industrial Chemicals and Intermediates
Antifreeze concentrates, brake fluids, heat-transfer fluids, unsaturated polyester resins, and technical-grade glycols can be characterized for DEG content as part of incoming-material verification or supplier qualification.
Testing Items
The assessment report typically covers the following measurable parameters, each with a defined regulatory benchmark:
- Total residual DEG content in polymers — expressed as percent by weight of PET, distinguishing free DEG from DEG chemically incorporated into the polyester chain.
- Specific migration of DEG into food simulants — expressed in mg/kg, determined under time and temperature conditions representative of the intended use. Under Commission Regulation (EU) No 10/2011 and the corresponding Chinese national framework (GB 9685, GB 4806.7), DEG is subject to a specific migration limit of 30 mg/kg food.
- DEG as an impurity in glycerin and propylene glycol — pharmacopeial monographs (USP-NF and the European Pharmacopoeia) restrict DEG to not more than 0.1% w/w, usually assessed together with ethylene glycol (EG).
- Combined DEG/EG screening — simultaneous quantification of diethylene glycol and ethylene glycol, and, where relevant, triethylene glycol and higher glycol homologues.
- Finished-product specification testing — verification against client-defined or regulator-defined acceptance criteria for the specific article under evaluation.
Testing Methods
Sample Preparation
Liquid samples (glycerin, syrups, e-liquids) are diluted in a suitable solvent and spiked with an internal standard prior to direct injection. PET and polyester matrices are decomposed by transesterification (methanolysis), aminolysis, or alkaline hydrolysis to liberate both free and chain-incorporated DEG, which is then extracted into an organic phase. Migration studies are performed by exposing the finished article to aqueous food simulants — for example 10% ethanol (simulant A), 3% acetic acid (simulant B), 20% ethanol (simulant C), and 50% ethanol (simulant D1) — under the contact regimes specified in EU No 10/2011, the EN 13130 series, and the GB 31604 series of national food-safety standards.
Gas Chromatography with Flame Ionization Detection (GC-FID)
GC-FID is the primary pharmacopeial technique for quantifying DEG and EG in glycerin and propylene glycol, offering robust quantification over the 0.01–0.1% w/w range and full compliance with the limit tests described in the relevant monographs.
Gas Chromatography–Mass Spectrometry (GC-MS)
GC-MS provides confirmatory identification through characteristic mass fragments, superior selectivity in complex matrices, and lower detection limits, achieving LOQs at the low mg/kg (ppm) level for migration solutions and extractables.
HPLC and Supplementary Techniques
High-performance liquid chromatography with refractive index detection (HPLC-RI) or evaporative light-scattering detection (HPLC-ELSD) is applied to thermally sensitive matrices, while quantitative 1H-NMR spectroscopy is an established approach for determining total co-monomeric DEG content in PET after dissolution of the polymer.
Method Validation and Quality Assurance
Validated methods include multi-point calibration with internal standardization, spiked recovery verification (typically 80–110%), replicate-injection repeatability, blank correction, and estimation of measurement uncertainty. Results are traceable to certified reference materials, and the testing is performed under ISO/IEC 17025-aligned quality systems in accredited third-party laboratories.
Applications
DEG residue assessment reports support a wide range of industrial and regulatory purposes:
- Packaging compliance — demonstrating that PET bottles, trays, and films meet the 30 mg/kg migration limit for food contact applications in the EU, China, and other regulated markets.
- Pharmaceutical quality control — releasing glycerin and propylene glycol lots under GMP and verifying conformance with pharmacopeial DEG/EG limits, in line with regulatory guidance on DEG-contaminated ingredients.
- Cosmetic safety assessment — verifying raw-material purity for toothpaste, mouthwash, and skincare products destined for international markets.
- Supplier qualification and incoming inspection — comparing incoming polymer or glycol lots against agreed specifications and building a documented compliance file.
- Regulatory submissions and audits — providing objective evidence for food-contact declarations of compliance, product dossiers, and customer or authority audits.
- Research and failure analysis — supporting root-cause investigation of contamination events, process optimization of polymerization conditions, and evaluation of recycled PET feedstocks.
FAQ
What is the acceptable limit for diethylene glycol residue?
It depends on the matrix. For glycerin and propylene glycol used in pharmaceuticals, pharmacopeial monographs limit DEG to not more than 0.1% w/w. For PET food contact materials, the specific migration of DEG into food simulants must not exceed 30 mg/kg under EU No 10/2011 and the corresponding Chinese national standards.
Why does PET contain DEG if it is restricted?
DEG is intentionally used as a co-monomer in PET production (typically up to about 3%) to control crystallization rate and improve processability. Because most of this DEG is chemically bound within the polymer chain, regulatory evaluation focuses on the fraction that can actually migrate into food, which is assessed through migration testing rather than total content alone.
What is the difference between DEG content testing and DEG migration testing?
Content testing measures the total amount of DEG present in the material itself (percent by weight), requiring chemical decomposition of the polymer. Migration testing measures how much DEG transfers from the finished article into food simulants under defined time and temperature conditions (mg/kg), and it is the parameter that regulatory limits are based upon.
Which analytical technique offers the best sensitivity?
GC-MS generally provides the lowest limits of quantification, in the low mg/kg range, together with confirmatory identification. GC-FID remains the reference method for pharmacopeial limit tests, while HPLC-RI and 1H-NMR are preferred for specific matrices such as thermally sensitive formulations and polymer-bound DEG determination.
What detection limits can be expected in the report?
For migration solutions and liquid matrices, validated GC-MS methods typically achieve LOQs at the low mg/kg level; for pharmacopeial limit tests in glycerin, the method reliably quantifies DEG down to well below the 0.1% w/w specification. Actual LOD and LOQ values are stated in each report for the specific method and matrix used.
How should a non-conforming result be handled?
If DEG exceeds the applicable limit, the report will clearly state non-conformity. Recommended follow-up actions include quarantine of the affected lot, extended sampling of retained and adjacent batches, traceability review of glycerin or monomer suppliers, and repeat confirmatory testing by GC-MS in an accredited third-party laboratory.