PBDE and PBB: Instrument Analysis for RoHS/WEEE Compliance Testing
Although the level of concern for PBDEs and PBBs is relatively high (i.e. as high as 0.1%), sensitive instrumental techniques are required to compensate for small sample masses often encountered, and to provide adequate sensitivity to get at least ten times lower than the action level. The buffer between the reported detection limit and the action level is important so false positives or negatives can be avoided. From an analytical chemistry standpoint, values reported near the detection limit are subject to considerable variability. Thus, ALS Environmental has designed an analytical approach that assures a high level of accuracy and precision at the action level.
The Gas Chromatography-Mass Spectrometry (GC-MS) procedures employed at ALS Environmental include Selective Ion Monitoring (SIM) and Large Volume Injection (LVI). The SIM mode allows dwelling on a particular ion so additional signal can be accumulated. The LVI allows a larger volume of sample extract to be delivered to the GC column. Together, the two techniques significantly improve sensitivity. Selectivity comes from the use of the MS.
For PBDEs, the entire range of bromine substitution is covered by the calibration curve. Although the number of congeners historically produced is limited (i.e. less than the 209 theoretically possible congeners), the calibration and identification scheme employed at ALS Environmental allows detection of any PBDEs present in the sample. The detection limit reported is calculated directly from the concentration of the lowest standard in the calibration curve. Note that a theoretical detection limit is also determined via precision measurements at the low end of the curve. These values are significantly lower than the limit derived from the low calibration point and serve as validation of the sensitivity of the procedure.
The analysis for PBBs is a bit more complex due to limited availability of PBB congeners. Currently, only the di- through hexa-, and the deca- are commercially available for use as calibration standards. (Note: ALS Environmental is currently having octa- synthesized). For detections of PBBs with those levels of substitution, fully quantitative results are possible. To provide identification and semi-quantitative information about hepta- and octa- substituted PBBs, commercial fire retardant mixes are analyzed. The commercial mixes have octa- present, as well as small amounts of hepta- and nona-. Semi-quantitative results for those congeners are derived from the response factor for hexa- substituted PBBs.