1,4-Dioxane Testing for Soaps, Shampoos, and Personal Care Products

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1,4-Dioxane Testing for soap, shampoo, and personal care products1,4-Dioxane (dioxane) is found in household products such as detergents, shampoos, body lotions, dishwashing soap, pharmaceuticals and cosmetics. It is a manufacturing by-product of the ethoxylation process. Ethoxylation is a chemical process in which ethylene oxide (1,2 epoxyethane) is added to fatty acids in order to make them more soluble in water. This process makes degreasing agents such as sodium lauryl sulphate less abrasive and gives products enhanced foaming properties. Unless removed under precise conditions, small amounts of dioxane are produced during ethoxylation. Dioxane, however, is unlisted in the ingredients of most products, as it is generally considered an accidental by-product of the production process. In personal care products dioxane enters the environment via waste streams, such as wastewater treatment plants and landfills. The U.S. Food and Drug Administration (FDA) has provided guidance to manufacturers about a process called “vacuum stripping” to help minimize the amount of dioxane in their final product. Manufacturers of personal care products should conduct laboratory analysis to determine the levels of dioxane in their products, and manufacturers using dioxane in their processes should analyze their waste streams for possible dioxane content.

Sample Matrix Test Method Reporting Limit*
Shampoos, Soaps and Personal Care Products EPA 8260B SIM, isotope dilution (headspace extraction) 5.0 **
Aqueous liquids EPA 8260B 100
Aqueous liquids EPA 8270C SIM, LVI and isotope dilution 1.0 ***
Soil and Sediment EPA 8270C SIM, LVI and isotope dilution 2.0 μg/Kg

* μg/L or ppb
** Due to the difficulty with some matrices a 5-fold dilution may be performed, resulting in an increased Method Report Limit of 25 ppb.
*** Lower detection limits are available.

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Analytical Methodology for Testing Soaps, Shampoos, and Personal Care Products

Complicated matrices like soap, shampoo and lotions can cause significant analytical problems, making it difficult to obtain accurate and reproducible sample concentrations, especially at lower limits of detection in the part per billion range. To address these issues, ALS Environmental uses a heated headspace sampler with a GC/MS. A sodium chloride-treated aliquot of sample is heated to drive the dioxane into a sample vessel’s headspace. This headspace sample is directly injected into the GC/MS in SIM mode to measure the dioxane concentration. The use of this method allows for a sufficient dynamic range and also decreases the time to reach equilibrium from one hour to less than 15 minutes. To enhance the accuracy and precision of the GC/MS SIM method, the labeled compound dioxane-d8 is used as the internal standard.

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