166

The  extraction  principles  were  similar  for  all  compounds.  While  solid  phase  extraction
(SPE)  with  a  polymer  resin  was  used  for  water  samples,  microwave  assisted  extraction
(MAE)  was  used  for  sediment  and  biota  samples  (6.3.2.1  and  6.6.3  to  6.6.5).
6.3.2.1  Methods  for  Chlorpyrifos,  Endosulfan  and  Trifluralin
GC-MS  analysis
A  common  GC-MS  analysis  method  is  used  for  all  three  matrices  (water,  sediment  and
biota).  Experimental  details  are  provided  in  the  appendix  under  6.2.
GC  analysis  using  a  standard  non-polar  capillary  column  was  unproblematic  and
yielded  baseline  separation  of  all  compounds.  MS  analysis  was  performed  both  in  El
and  NCI  mode.  The  parameters  for  GC  and  MS  are  summarised  in  Table  82  (chapter
6.6.2).
Deuterated  analogues  of  trifluralin,  chlorpyrifos  and  endosulfan  I  were  used  as  internal
standards  for  quantification.
As  has  been  demonstrated  in  the  chapter  on  validation  (6.3.3),  the  NCI  method  was
more  sensitive  with  all  compounds,  and  was  consequently  used  to  analyse  all  samples.
Apart  from  the  inherently  high  sensitivity  of  the  NCI  method  for  pure  standard
solutions,  it  was  found  to  have  additional  advantages  in  real  samples  with  matrix
underground.  Due  to  its  high  selectivity,  all  MS  traces  showed  very  clean  baselines  with
little  chemical  noise.  Examples  of  this  are  shown  in  Figure  29.