Appendix C Analytical equipment and procedures
During the project it has become clear that a portable X-Ray Fluorescence (XRF) analyser has the required sensitivity to detect bromine present in the BDE’s at levels common in polymers.
Figure 9. X-ray fluorescence principle
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Figure 9 is a diagrammatic representation of how X-ray fluorescence works. Electron shells K, L and M are represented by yellow, blue and green spheres respectively. When excited, electrons move between these shells and the resulting nature of the X-ray spectrum energy emitted is characteristic of the element.
The X-ray fluorescence principle is depicted in the figure above Footnote 18. An inner shell electron is exited by an incident photon in the X-ray region. During the de-excitation process an electron is moving from a higher energy level to fill the vacancy created by the ejection. The energy difference between the two shells appears as an X-ray emitted by the atom. The X-ray spectrum acquired by the instruments detector during this process reveals a number of characteristic peaks. The X-ray frequency identifies the elements in the sample, while the energy of each peak identifies the quantity of that element present.
The XRF analysers have the advantage of being non-destructive, multi-element, fast and cost-effective. It also provides a fairly uniform detection limit across a large portion of the periodic table for elements heavier than fluoride and is applicable to a wide range of concentrations from 100% to a few parts per million. Another advantage is that the detector has no ‘memory’, i.e. samples with very low concentrations can be analysed immediately after a sample with a very high concentration which would be impossible using a gas chromatograph for example.
Bromine constitutes up to 80% of the BDE weight and flame retardants are often used in a concentration of 0.1 – 30% of the final polymer. Therefore a hand held XRF analyser with a detection limit of 10 ppm (0.001 %) has the required sensitivity to detect brominated compounds in the polymers. A small drawback is that an operator will need a licence from the National Radiation Laboratory to operate a XRF analyser.
Figure 10. Schematic diagram of the prototype instrument TIAS-254 with IAMS
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Figure 10 is a diagrammatic representation of an ion-attachment mass spectrometer (IAMS). The particular instrument illustrated is referred to as prototype TIAS-254 and its operation is explained in the text.
Another analytical instrument is an ion-attachment mass spectrometer (IAMS). The principle is shown in the figure aboveFootnote 19 This is a form of mass spectrometry that uses a "soft" form of ionization similar to chemical ionization in which a cation is attached to the analyte molecule in a reactive collision: M + X+ X A → MX+ + A where M is the analyte molecule, X+ is the cation and A is a non-reacting collision partner. As cation an alkali element is used such as sodiumFootnote 20 or lithium.
Currently, IAMS is used industrially to verify, with a high throughput, the concentrations of brominated flame retardants (BFR) in plastics in compliance with European RoHS (Restriction of Hazardous Substances) regulation in place since 2006. The banned molecules include PBB and PBDE, whose concentration should not exceed 0.1% w/wFootnote 21 IAMS was originally developed by Prof. Toshihiro FUJIIFootnote 22
Figure 11 IAMS analyser prototype
BFR analysis in water requires far lower detection limits, however as is shown in section 2 above bromine present in leachate can be analysed when concentrated. This can be on filter paper where all small particulates with adsorbed bromine containing compounds or in a solid phase extraction gel which adsorbs non-polar organic compounds. At high enough concentration and sufficiently concentrated the bromine can be detected using XRF or IAMS analysis.
However to distinguish between all different types of BFRs far more complex analysis is required. A wide range of methods to determine residues of PBDE in various media (air, sewage sludge, sediment, human adipose tissue, marine organisms, fish, and feed) have been developed. In general the samples are extracted using common solvents like hexane, acetone, chloroform or methylene chloride, however, sometimes the extraction fluid needs to be more exotic like hot concentrated sulphuric acid, tetrahydrofuran or potassium oxalate/ethanol/diethyl ether/pentane.
The extraction is followed by a clean-up phase, often on Florisil, followed by quantification by GC/MS (Gas Chromatography/Mass Spectroscopy), HPLC (High Pressure Liquid Chromatography), GC/MS-SIM/NCI ( Selective Ion Monitoring / Negative Chemical Ionisation), LC/MS (Liquid Chromatography), HRGC/HRMS (High Resolution Gas Chromatography/High Resolution Mass Spectroscopy), GPC (Gel Permeation Chromatography), etc.
All of these require high quality standards and for many of the brominated flame retardants these are not available for every congener or isomer.
