10

2.1.1  Analysis
2.1.1.1  GC  screening
Light  fuel  oil  is  easily  detected  in  GC  screening  because  of  its  limited  boiling  range:
compounds  end  at  about  n-C25.  This  n-alkane  has  a  boiling  point  of  about  400  °C  (Fig.  2).
Accordingly,  the  possibilities  of  comparing  two  light  fuel  oil  samples  are  rather  limited.
Weathering  effects,  which  are  quite  common  (see  above),  are  even  more  severe  in  this  case
because  they  lead  to  further  limitations  in  sample  comparison.
Light  fuel  oil  samples  can  be  differentiated  by  the  shapes  of  the  envelopes  of  the  n-alkanes,
the  shapes  of  the  envelopes  of  the  “unresolved  complex  mixture”  (UCM),  which  mainly
consists  of  naphthenes  (cyclo-alkanes),  and  their  Cn/pristane,  Cis/phytane,  and
pristane/phytane  ratios  (Fig.  2  and  Fig.  3).

Fig.  2:  Gas-chromatogram  of  a  typical  light  fuel  oil.  The  envelopes  of  the  n-alkanes
and  the  UCM,  Cn,  pristane,  Cis,  phytane  and  C25  (computer  calculations)
are  shown.

A  Given  here  is  the  general  evaluation  of  the  GC  screening  results  of  oil  samples
(“first  look”).  Further  peaks  appearing  in  between  the  homologues  series  of  the  nalkanes,
  such  as  nor-pristane,  further  isoprenoids  and  pronounced  naphthenes,
might  provide  further  information  if  present.