The gas chromatography/chemical ionization mass spectrometry (GC/CI-MS) is carried out using a ThermoFinnigan Polaris Q mass selective detector connected to a ThermoFinnigan TraceGC gas chromatograph equipped with a capillary Rtx-5MS column (15 m x 0.25 mm; 0.25 µm coating thickness; Resteck). Helium is used as a carrier gas at a flow rate of 1 ml/min. The temperature gradient is as follows: 60 °C for 1 min, 60 – 180 °C at 25 K/min, 180 – 270 °C at 5 K/min, 270 °C for 1 min, 270 – 300 °C at 10 K/min and 300 °C for 20 min. The detection occurs by negative chemical ionization with ammonium as ionization gas. Electron energy of 100 eV, an ion source temperature of 200 °C, and a temperature of 300 °C for the transfer line are used.
For quantification, the ions m/z 141 (D 6 -SA), 137 (SA), 215 (D 6 -JA), 209 (JA), 296 (D 5 -oPDA), 291 (oPDA), 263 (dinor-oDPA), 509 (D 5 -12-oxo-13-hydroxy-18:2), 506 (12-oxo-13-hydroxy-18:1 and 10-oxo-9-hydroxy-18:1), 504 (12-oxo-13-hydroxy-18:2 and 10-oxo-9-hydroxy-18:2) are used, respectively. 100 ng of deuterium-labeled compounds are added to the sample at the beginning of the extraction.
standards are available from Sigma ( Germany ) Larodan ( Sweden ), Cayman Chemical (USA), kindly provided by Mats Hamberg ( Stockholm , Sweden ) and Otto Miersch (Halle/Salle, Germany ) or enzymatically synthesized, respectively
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