Until the early 2000’s, 1,4-dioxane has received little attention from regulatory agencies. This compound is a frequent contaminant of concern at sites contaminated with chlorinated compounds, due to its widespread use as a stabilizer for chlorinated solvents. No federal maximum contaminant level in drinking water has been established, however some state agencies have set action limits as low as 0.25 µg/L (i.e., New Hampshire). Recently, the ITRC has issued several 1,4-Dioxane fact sheets, available at: https://14dx-1.itrcweb.org/
Analytical Methods
There are three methods typically used for the analysis and quantitation of 1,4-dioxane, and there are pros and cons to each. Depending on your goals, you might choose either SW-846 Method 8260 SIM with isotope dilution, SW-846 Method 8270 SIM with isotope dilution, or EPA Method 522 SIM.
Method 8260 SIM – This method involves purging 1,4-dioxane from a water sample, with an inert gas, and trapping it for analysis, and is best suited for samples with high concentrations. Due to 1,4-dioxane’s poor purge efficiency, the reporting limit (RL) is typically higher than methods that don’t relying on purging. This method is also subject to interferences from chlorinated solvents. Low concentrations of 1,4-dioxane reported by this method are questionable, at best.
Method 8270 SIM –This method can achieve lower RLs because it relies on solvent extraction from a sample, and evaporative concentration, instead of purging. It is a better choice than Method 8260 for low concentrations of 1,4-dioxane but can be subject to losses during the extraction and concentration steps.
Method 522 SIM – This method is designed specifically for the analysis of low concentrations of 1,4-dioxane in drinking water. This method uses solid phase extraction (SPE) to extract and concentrate dioxane on a solid adsorbent material. It is not subject to the purging and extraction issues that Method 8260 and Method 8270 have, which allows for achieving lower RLs. At this time, there may be fewer laboratories certified for this method than for Methods 8260 and 8270.
1, 4-Dioxane is completely miscible in water, which causes poor purging and results in high detection limits when using methods designed for analyses of volatile compounds. In addition, those methods do not require the use of 1,4-dioxane-d8 as a labeled analog to monitor and correct for purge inefficiencies. 1,4-Dioxane-d8 is a man-made chemical in which all eight hydrogens are replaced with deuterium, allowing the two compounds to be differentiated by a mass spectrometer (MS). The labeled compound responds to the analytical system in the same manner as the unlabeled native compound, 1,4-dioxane. As a result, recovery of 1,4-dioxane in the sample can be corrected for the percent recovery (%R) of the labeled compound, thereby adjusting it to the actual concentration in the sample. This mode of quantitative analysis is called isotope dilution and is used to improve the representativeness of the reported concentration of the contaminant compound to what is really present at the site.
Considerations
There are other considerations that will influence the appropriate method for your project. These include:
- The presence of other site compounds at concentrations that render a low RL for 1,4-dioxane unnecessary;
- Project-specific clean-up criteria that dictate the RL required; and
- Previously approved site-specific documents that define the analytical method to be used.
Communication with the laboratory is vital when selecting your method. If Method 8260 or Method 8270 are options, confirm with the laboratory that they are using 1,4-dioxane-d8 as an a recovery standard and performing isotope dilution methodology. If isotope dilution is not performed, and 1,4-dioxne was included as a conventional surrogate, the correction based on the recovery of the 1,4-dioxane-d8 can be performed by the data user. The laboratory RL, not the method detection limit (MDL), must meet the site clean-up criteria. The MDL is a statistically generated number and is not supported by the reported data. Use caution when comparing historical 1,4-dioxane data generated by one method with data generated using other techniques, because such a comparison may not be accurate, due to the limitations described above.
References
United States Environmental Protection Agency, Office of Solid Waste and Emergency Response (5106P), EPA 505-F-14-011, November 2017.
SW846 – Method 8260D: Volatile Organic Compounds by Gas Chromatography/Mass Spectrometry (GC/MS)
SW846 – Method 8270E – Semivolatile Organic Compounds by Gas Chromatography/Mass Spectrometry (GC/MS)
1,4-Dioxane Web-based Facts Sheets, ITRC. https://www.itrcweb.org/
For more information, contact: ecsteam@ddmsinc.com