On European level Commission Regulation (EC) No 1883/2006 of 19 December 2006 lays down methods of sampling and analysis for the official control of levels of dioxins and dioxin-like PCBs in certain foodstuffs.
Confirmatory methods are methods that provide full or complementary information enabling the dioxins and dioxin-like PCBs to be identified and quantified unequivocally at the level of interest. These confirmatory methods have to fulfil the following requirements:
- Confirmatory methods are high-resolution gas chromatography/high resolution mass spectrometry (HRGC/HRMS) methods.
- Basic criteria:
- High sensitivity and low limits of detection: For dioxins and non-ortho PCBs detectable quantities have to be in the picogram TEQ (10-12 g) range. PCBs are known to occur at higher levels than the PCDD/Fs and non-ortho PCBs. For most PCB congeners sensitivity in the nanogram (10-9 g) range is already sufficient.
- High selectivity (specificity): a distinction is required for PCDD/Fs and dioxin-like PCBs from a multitude of other, coextracted and possibly interfering compounds present at concentration up to several orders of magnitude higher than those of the analytes of interest.
- High accuracy (trueness and precision): the determination shall provide a valid estimate of the true concentration in a sample.
- Addition of 13C-labelled 2,3,7,8-chlorine substituted internal PCDD/F standards and of 13C-labelled internal dioxin-like PCB standards: at the beginning of the analytical method e.g. prior to extraction in order to validate the analytical procedure. There is a clear preference, certainly for confirmatory methods, of using all 17 13C-labelled 2,3,7,8-substituted internal PCDD/F standards and all 12 13C-labelled internal dioxin-like PCB standards.
- For foodstuffs of plant origin and foodstuffs of animal origin containing less than 10 % fat, the addition of internal standards is mandatory prior to extraction. For foodstuffs of animal origin containing more than 10 % fat, the internal standards may be added either before extraction or after fat extraction.
- Prior to GC/MS analysis, 1 or 2 recovery (surrogate) standard(s) must be added.
- Control of recovery is necessary. For confirmatory methods, the recoveries of the individual internal standards shall be in the range of 60 to 120 %.
- Separation of dioxins from interfering chlorinated compounds such as non-dioxin like PCBs and chlorinated diphenyl ethers has to be carried out by suitable chromatographic techniques (preferably with a florisil, alumina and/or carbon column)
- Gas chromatographic separation of isomers has to be sufficient
- Determination: tetra- through octa-chlorinated dioxins and furans by isotope dilution HRGC/HRMS.
Other methods available
US EPA Method 8290A: Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) by high-resolution gas chromatography/high resolution mass spectrometry (HRGC/HRMS) – Determination in fish tissue
US EPA Method 1668B: Chlorinated biphenyl congeners in water, soil, sediment, biosolids and tissue by HRGC/HRMS – determination of dioxin-like and non-dioxin like PCBs in fish tissue.
US EPA Method 1613: Tetra- through Octa-chlorinated dioxins and furans by isotope dilution HRGC/HRMS. This method is for the determination of tetra- through octa-chlorinated dibenzo-p-dioxins and dibenzofurans in water, soil, sediment, sludge, tissue (fish) and other sample matrices by high resolution gas chromatography/high resolution mass spectrometry (HRGC/HRMS).
Alternative methods from literature
Different methods are used to determine the levels of PCDD/Fs and dioxin-like PCBs in environmental as well as in food and feed matrices. A distinction is made between the so-called ‘reference method’ and the alternative or screening methods. Gas chromatography (GC) in combination with high resolution mass spectrometry (HRMS) is used as the reference method (‘the golden standard’) for the identification and quantification of PCDD/Fs and dioxin-like PCBs (Vromman et al., 2012).
The analytical procedure for the determination of PCDD/Fs and dioxin-like PCBs consists of the following steps:
- a. Extraction of fat
- b. Purification of the fat extract
- c. Measurement by GC-HRMS