Distribution of Chlorinated Hydrocarbon Pesticides and PCBs in the ...

f) sediment samples
Precision of chlorinated pesticide analyses and accuracy
of PCB analyses were determined by six replicate analyses of
the standard reference sediment CS-1, a coastal marine sediment
reference sample supplied by the National Research Council of
Canada, Marine Analytical Chemistry Standards Progam (NRCC/MACSP)
certified at 1.2 k0.6 ng/g PCB quantitated as Aroclor 1254.
This SRM is certified only for PCBs as Aroclor 1254 determined by
packed column GC methodstand no data is available on the levels
of chlorinated pesticides. Consequently, the SRM allows a method
validation only for PCBs. The analyses of the SRM were carried
through with several sediment sample batches to monitor batch to
batch variation in extraction efficiency and the results given in
Table 3.13. The mean concentration of Aroclor 1254 from six
determinations of the SRM was 0.75 k0.05 ng/g, lower than but
within the uncertainty of the certified concentration of 1.2
k0.6ng/g. The lower values found by Arctic Labs are attributed to
the analysis by capillary GC which is has higher resolution and
specificity than the packed column technique used for the SRM
certification. The results for other chlorinated compounds found
in CS-1 are given in Table 3.13 and indicate the precision at
this level.
The extraction efficiency of the sediment method was
verified by exhaustive Soxhlet extraction (25h with 1:l
acetone/hexane) of the SRM sediment after analysis by the
standard method. The results indicate that for those compounds
found and quantified in the SRM, the standard method extracted
92-99% of the organochlorines present, and an additional 1-8%
could be extracted by soxhlet from the SRM sample residue. The
residual levels extracted by soxhlet are close to or below
detection and quantification limits and no correction for
extraction efficiency to the sediment concentrations was made.