OCPs in cod liver oil

Samples of cod were taken from the North Sea and frozen immediately after capture and transported at -25°C. They were stored at this temperature until they were defrosted prior to the preparation of the oil material. The cod livers were carefully dissected and cooked in water for 30 min. The upper layer of cod liver oil was centrifuged twice, once to remove solid particles, and a second time to remove water. The oil was mixed and collected in a clean round-bottomed flask under argon while it was still hot. 

The cod liver oil reference material was produced by mixing two different previously characterised cod liver oils. The mixing enabled to reach a medium level of OCP contamination, compared to usually analysed samples. 

5 L of a highly contaminated cod liver oil (A) was mixed with 4.8 L of a relatively uncontaminated cod liver oil (B) in a 10 L reagent bottle by means of a mechanical stirrer. Prior to mixing, 200 mL of oil (B) was gently heated to 60°C to dissolve 2.5 g 

Butylated Hydroxy Toluene (BHT) used as an antioxidant. The aliquot was cooled, returned to the bulk and mixed by stirring. 

The stability of the organochlorine pesticides in the cod liver oil was studied at three temperatures (-20°C, +20°C and +40 C) after 1, 3, 6 and 12 months, using the same method as applied in the homogeneity study. Due to an interference with toxaphene, the results of the measurement of y-chlordane were found to be unrealistic. Therefore, the stability of this compound could not be demonstrated. As for o,p -DDE the origin of the unreliability of the results is due to the instability of o,p -DDT in the analytical system, both compounds were not considered for certification. For the remaining OCPs no instability could be demonstrated. 

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