sentence: The samples were heated in the UltraClave IV ( EMLS , Leutkirch , Germany ) using the following program : Step 1 : 5 min => 80 ° C ; step 2 : 15 min => 150 ° C ; step 3 : 15 min => 250 ° C ; step 4 : 30 min at 250 ° C. For the sulfur determination an Agilent 7500ce at m / z 34 system was used .