Analysis of Ethylene Glycol and Diethylene Glycol in Oral Syrup Containing Glycerin

Importance of the topic

Analysis of ethylene glycol (EG) and diethylene glycol (DEG) in glycerin-containing oral syrups is critical for pharmaceutical safety and regulatory compliance. Contamination by these glycols has caused serious adverse events historically, so sensitive, reliable testing methods are required for routine quality control, batch release, and forensic investigation. The method described demonstrates a targeted GC/MS approach capable of meeting FDA-recommended performance criteria for EG/DEG detection in complex syrup matrices.

Study objectives and overview

The primary objective was to optimize and demonstrate a GC/MS method (Agilent 8890 GC coupled to Agilent 5977C MSD) for detecting and quantifying EG and DEG in oral syrup formulations that contain glycerin. Key performance targets included achieving an instrument limit of quantification (iLOQ) at 0.1 ppm, acceptable precision for replicate standards, and a practical sample preparation workflow compatible with syrup matrices.

Methodology

Sample preparation and standards:

• Stock standards for EG and DEG prepared at 1 mg/mL in methanol.
• Internal standard (2,2,2-trichloroethanol) prepared at 1 mg/mL in methanol; used for internal standard calibration.
• Working QC standard prepared by dilution to yield standards in the calibration range; internal standard added to all standards and samples.
• Drug product samples: 1.0 g of syrup/solution/suspension weighed into a 10 mL volumetric flask, 0.1 mL of internal standard solution added, diluted to volume with methanol, vortexed; samples with particulates filtered through 0.20 µm PTFE syringe filters prior to analysis. (Nylon filtration was also referenced for some steps.)

Chromatography and mass spectrometry conditions:

• Instrument: Agilent 8890 GC system coupled with Agilent 5977C single‑quadrupole MSD operating in SIM mode.
• Analytical column: DB-WAX, 30 m × 0.25 mm, 0.50 µm film.
• Injection: 1 µL, split 20:1; inlet temperature 240 °C; helium carrier at 1.0 mL/min (constant flow).
• Oven program: start 130 °C (4 min), ramp 17 °C/min to 195 °C (4 min), then 35 °C/min to 240 °C (4 min).
• MS transfer line 240 °C; ion source 230 °C; quadrupole 150 °C; monitored SIM ions: m/z 31, 33, 43, 75, 113.
• Calibration: solvent-based curve from 0.1 to 4 ppm with internal standard normalization.

Used instrumentation

• Agilent 8890 Gas Chromatograph.
• Agilent 5977C Single‑Quadrupole GC/MSD.
• DB‑WAX GC column (30 m × 0.25 mm, 0.50 µm, p/n 122‑7033).
• Standard laboratory equipment for volumetric preparation, vortex mixing, and syringe filtration (PTFE 0.20 µm filters).

Main results and discussion

The method achieved an instrument limit of quantification (iLOQ) of 0.1 ppm for both ethylene glycol and diethylene glycol, consistent with FDA guidance expectations. Precision was excellent for the working standards: percent relative standard deviation (%RSD) for peak area across six replicates was 1.83% for EG and 1.58% for DEG; %RSD of internal standard area across six replicates was 1.81% for both analytes. Solvent-based calibration was linear across 0.1–4 ppm using internal standard calibration. Representative chromatograms demonstrated clear EG and DEG peaks at the 0.1 ppm level with baseline resolution from matrix components, and the selected SIM ions provided specific and sensitive detection.

Benefits and practical applications

The developed GC/MS procedure offers a sensitive, robust, and relatively rapid workflow suitable for routine QC laboratories in pharmaceutical and biopharmaceutical settings. Advantages include:

• Low quantification limits (0.1 ppm) that meet regulatory safety thresholds.
• Simple sample preparation (methanol extraction and filtration) compatible with viscous glycerin-containing syrups.
• Good precision and reproducibility demonstrated by low %RSD values.
• Use of an internal standard to control for injection and matrix variability.

Use cases include routine batch testing, stability and release testing, investigations of suspected contamination, and regulatory compliance testing in accordance with FDA recommendations.

Future trends and potential applications

Potential directions to enhance and extend this method include:

• Automation of sample preparation and on-line filtration to increase throughput and reduce manual variability.
• Exploration of alternative separation or detection techniques (e.g., LC‑MS/MS with high‑resolution mass spectrometry) for confirmatory analysis or even lower detection limits in highly challenging matrices.
• Method miniaturization and microsampling approaches for limited-volume or field testing scenarios.
• Implementation of chemometric or advanced data-processing workflows for improved deconvolution of coeluting matrix components.
• Harmonization of regulatory acceptance criteria and multi-lab validation to broaden method adoption across different markets.

Conclusion

The validated GC/MS approach using the Agilent 8890/5977C platform provides a fit-for-purpose analytical solution for quantifying ethylene glycol and diethylene glycol in glycerin-containing oral syrups. With an iLOQ of 0.1 ppm, tight precision, and a straightforward methanol extraction protocol, the method supports routine safety testing and regulatory compliance. The combination of SIM detection and internal standard calibration yields reliable sensitivity and reproducibility suitable for QC laboratories.

Reference

1. U.S. Food and Drug Administration. Gas Chromatography–Mass Spectrometry (GC‑MS) Method for the Determination of Ethylene Glycol (EG) and Diethylene Glycol (DEG) in Cough, Cold, and Allergy Products Containing Glycerin. FDA Laboratory Methods 2025.