Manufacturer of Natural Products That Empower People to Live Healthier Lives
Nutrition for Optimal Wellness
Glycerin or Diethylene Glycol?
By Heidi Li, Method Development Scientist [former], Quality Control Department, NOW Foods
Diethylene glycol (DEG), also known as "diglycol" or "diglycol stearate", has been recently identified as a possible adulterant or substitute for glycerin in the preparation of medicine and foods, but it is believed to have caused hundreds of deaths and injuries in numerous countries over a number of years.  Glycerin is a sweetener commonly used worldwide in the manufacturing of medicinal syrups for over-the-counter and prescription drugs.  It has also been used in many formulations of cosmetic and food products, including liquid dietary supplements.  DEG is used as a solvent in antifreeze blends.  Ingestion of DEG may cause abdominal pain, nausea, vomiting, dizziness, and decreased urine production.  If not promptly and adequately treated, severe kidney damage and liver injury may also occur.
DEG-contaminated glycerin may unintentionally be accepted for use in manufacturing pharmaceuticals and foods. DEG poisoning is becoming an important public safety issue. The investigations reported that DEG-related poisonings in various countries were due to lack of testing for contamination, as well as lack of other manufacturing quality control measures. The most recent incident of DEG-contaminated cough syrup occurred in Panama.  The investigation uncovered that the reason for the contamination was similar to other cases: the manufacturers did not conduct full identity tests on the raw materials imported, and relied on unreliable certificates of analysis submitted by suppliers.
Such incidents will continue to occur until the resources are appropriated to stop it. It is critical that all manufacturers, as well as others that use glycerin to prepare drug and food products, must understand the utmost importance of detecting DEG contamination in glycerin. The relevant ingested level of DEG considered safe for humans is 0.1%, as recommended by the interagency DEG Contamination Workshop of 1997.  Recently, the Food and Drug Administration (FDA) issued a guidance that requires manufacturers to test for DEG in glycerin and glycerin-based raw materials to ensure the DEG content is at 0.1% or less before the materials are used to manufacture finished products. The recommended methods by FDA include limit and identity tests listed in the United States Pharmacopeia (USP) monograph for glycerin or a thin-layer chromatography testing method published in the Journal of AOAC International.
At NOW® Foods, we perform identity testing on our raw materials and finished goods in accordance with Good Manufacturing Practice standards to ensure the safety and quality of our products. To avoid the use of DEG-contaminated glycerin, specific analytical testing procedures are performed on glycerin materials, as well as finished products containing glycerin such as our XyliWhiteTM toothpastes. These quality controls provide assurance that our products are tested to be safe.
Technical Details
The USP infrared absorption method from the USP monograph is used for the identification of individual compounds of glycerin and DEG.  The USP gas chromatography/flame ionization selection (GC/FID) method is used to distinguish glycerin from DEG and determine the concentration of DEG contamination.  We use the USP GC method to determine the level of DEG in glycerin by spiking 0.1% of DEG into glycerin standard solution and comparing the peak size. The assay allows the precise and sensitive identification and limit testing of DEG in glycerin raw material and some final products.  By using this method to verify the limit of DEG in glycerin products, Now Foods ensures the best quality of our products for our customers, while avoiding potentially harmful impurities.
1  J.M. Mathews, M.K. Parker and H.B. Mathews, Metabolism and disposition of
diethyelene glycol in rat and dog, Drug Metabol. Dispos. 19 (1991) (6), pp. 1066–1070.
2  Limit of diethylene glycol and related compounds, Glycerin / Official Monographs, the  United States Pharmacopeia 29, page 1011
3  Testing of glycerin for diethylene glycol, Guidance fro Industry, Food and Drug Administration