Abstract
Polybrominated diphenyl ethers (PBDEs) are additive flame retardants that are used in many household and office products, including furniture, electronics, and textiles. These lipophilic compounds have been found to be persistent and bioaccumulative in nature. Due to their toxicity and ubiquitous presence, PBDEs are included in many monitoring efforts across a wide array of biological and environmental sample matrices. The analysis of PBDEs is challenging due to structural isomers that need to be chromatographically separated and thermally-labile compounds of interest that may breakdown during gas chromatography. Furthermore, nonvolatile material may still persist even in cleaned final extracts, requiring GC column and inlet maintenance to be performed. PBDEs included in EPA Method 1614 are well resolved on a 15 m x 0.25 mm x 0.10 μm Rtx®-1614 GC column that was specifically designed to meet method resolution requirements of less than 40% valley height between BDE 49 and BDE 71. The selectivity of this column, in combination with properly translating the original GC method, allowed the column to be trimmed significantly for maintenance (7.9 m) while maintaining the method resolution criterion. This allows chromatographers to extend GC column lifetime.
Introduction
Flame retardants have been added to numerous products including polyurethane foams, electronics, plastics, and carpet padding to reduce the risk of burning. Technical mixtures of polybrominated diphenyl ethers (PBDEs) have been extensively used as additive flame retardants since the 1970s [1]. However, the technical mixtures containing penta and octa congeners were voluntarily withdrawn in the United States in 2005 and the last remaining PBDE mixture, decaBDE, is being phased out. Unfortunately, the concentrations of PBDEs in the environment have not been declining and, due to their persistent and bioaccumulative nature, these compounds are still widely monitored. The health concerns of PBDEs are similar to that of polychlorinated biphenyls (PCBs) and at the most recent Stockholm Convention on Persistent Organic Pollutants, two technical mixtures (pentaBDE and octaBDE) were added to the priority pollutant list [2]. Monitoring PBDEs in biota and environmental matrices can be difficult due to the complexity of the sample, structural isomers that must be separated chromatographically, and thermally-labile compounds that can break down during gas chromatography (GC). A 15 m x 0.25 mm x 0.10 μm Rtx®-1614 GC column, a 5% diphenyl, 95% dimethyl polysiloxane type stationary phase, was specifically designed by Restek to meet EPA Method 1614 resolution requirements for critical isobaric BDE congeners 49 and 71 [3]. Using a short, thin-film column also allows the elution of decabromodiphenyl ether (BDE 209) without on-column thermal degradation that can compromise its qualitative and quantitative determination [4]. GC column and inlet maintenance is especially important for BDE analysis, because nonvolatile material persists in sample extracts and deposits onto the front of the column and liner. This can cause poor transfer of BDEs to the GC column, which compromises quantification and sensitivity. That same material at the head of the GC column also leads to poor peak shapes and reduced resolution between critical congeners, such as BDEs 49 and 71. Trimming a coil (0.5 m to 0.7 m) off the front of the column and changing the inlet liner restores performance and significantly increases the column lifetime. While fewer column changes saves time and money, care must be taken to properly translate the method for the shorter column length to ensure that the original separation is maintained. If the GC method is not translated after the column has been trimmed, the column flow would be very fast, which would decrease resolution and detectability. The flow may also exceed the pumping capacity of many mass spectrometers. Method translation software can help users adjust the GC oven program for the shorter column length and maintain the elution profile of the original chromatogram. Using a 15 m x 0.25 mm x 0.10 μm column, we investigated how much of the GC column could be clipped off for maintenance before the Method 1614 resolution requirement for BDE 49 and BDE 71 could no longer be met.>> Download the full Application Note as PDF
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