Overcoming analytical challenges of Other Test Method 50: Analysis of volatile fluorinated compounds in passivated...

The production and emission of per- and polyfluoroalkyl substances (PFAS) has become a cause of concern due to their environmental persistence, accumulation, and potential health impacts. There are few methods for measuring air emissions of PFAS from fluorochemical manufacturing facilities and products of incomplete combustion or destruction (PICs/PIDs) that may be formed during incineration of PFAS-containing materials. The U.S. Environmental Protection Agency (EPA) developed Other Test Method (OTM)-50, a canister sampling and thermal desorption-gas chromatography/mass spectrometry (TD-GC/MS) analysis method for measuring volatile fluorinated compounds (VFCs) from stationary source emissions. Here, we describe the experiments that were conducted to develop the optimized analytical methods for samples that may contain high humidity and carbon dioxide (CO₂) levels. A prototype preconcentrator with a focusing trap capable of reaching -100 °C was used to improve retention of tetrafluoromethane (CF₄), but the lower temperature also trapped more CO₂, which caused signal suppression of CF₄ as well as hexafluoroethane, chlorodifluoromethane, tetrafluoroethene, and trifluoromethane. Therefore, the optimized method utilized a low trap temperature of -30 °C to avoid trapping high levels of CO₂ that may be present in stationary source samples. We found that increasing the dry purge time to nine minutes during preconcentration eliminated enough CO₂ to recover target compounds within ±30 % of the standard value, as required by OTM-50. The method was used to analyze samples collected in the absence and presence of high CO₂ levels to demonstrate the precision of the method even under challenging conditions.