CBs in sewage sludge

The final solution was injected (2 pL) onto a 50 m fused silica capillary GC column. The GC conditions are described in details elsewhere [21]. The calibrants (BCR CRM Nos 291, 293, 294, 295, 296, 297 and 298) and blanks were treated in exactly the same way as the samples. The recoveries of the CBs varied between 80% and 100%. The determination of each CB was verified to be completed within the linear range of the ECD detector. 

The stability was tested at -18°C, +20°C and +37°C by analysing the material at the beginning of the storage period and at the end of the certification campaign (36 months after the first analysis). The same analytical method as the one used for the homogeneity study was applied. No instabililty could be demonstrated for any of the CB determined. It was observed that the repeatability of the methods was significantly better after three years, which was the result of the participation in interlaboratory studies [21,23]. 

The final determination of the CBs was performed by capillary gas chromatography with electron capture detection mass spectrometry was used as complementary technique to confirm the identity of each of the CBs determined. Each participant had validated its method by performing experiments on recovery, extraction efficiency, procedure blanks and detector linearity. The seven individual CB calibrants were supplied to the participants as pure, crystalline CRMs from BCR (CRMs Nos. 291,293, 294,295, 296. 297 and 298). Each laboratory was requested to prepare separate calibration solutions of the appropriate concentration, in iso-octane, to calibrate the detector and lying within its linear range. The use of at least one internal standard was mandatory the participants, however, were left free to select the internal standard(s) best suited to their methods. They had to verify that the selected compounds did not occur in the candidate reference material or did not interfere with compounds present in the material. A series of pure dichlorobenzylalkyl ethers (DCBEs) was made available to the participants but other internal standards were also accepted of which the list is given in the certification report [21] along with additional details on calibration procedures. 

Details on the methods used (extraction, clean-up, separation) are given in the certification report [21]. Extraction was either carried out ultrasonically or by Soxhlet 

The identity of the other measured CBs was confirmed by GC-MS. The six other compounds (CBs 28, 52, 101, 118, 153 and 180) were certified and the values are given in Table 10.6 along with their uncertainties. 

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