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CH 2 Cl2/CH 4 -NICI:
Advantages:
• Interferences from other polychlorinated compounds (pesticides, PCB) strongly suppressed.
• Response factor of formula groups and between congener groups rather uniform.
• Only [M+Cl]" ions are formed, interferences by mass overlap minimised.
• Lower chlorinated formula groups (CI3 and CI4) detectable.
• Use of LRMS possible.
Disadvantages:
• Rather quick contamination of ion source, therefore mainly suited for record of complete formula
group patterns and quantification of selected samples with high content of interferences (sediments).
EI-MS/MS:
Advantages:
• Selection of fragment ions in common to all PC As formula groups such as [CsHvCl]" 1 " and
further fragmentation to e.g. [CsH 5 ] + allows to detect all PCAs simultaneously (sPCAs and
mPCAs).
• Systematic errors due to strong influence of degree of chlorination on response factors
eliminated or reduced.
• Inexpensive instrumentation such as an ion trap mass spectrometer can be used (costs €
60'000.-)
• Limits of detection sufficient for biota, but can be lowered further (factor of 4-5) using
more expensive triple quadrupole mass spectrometry (LRMS). Desirable for sediments of
low PCA content.
• Ideal for quick screening and pre-selection of samples for further specific formula and
congener group analysis.
Disadvantages:
• Only the sum of sPCAs and mPCAs can be determined.
• No differentiation between formula and congener groups possible.
ECNI-MS with response factor correction
Advantages.
• Systematic errors of quantification due to different degree of chlorination between sample
and reference can be compensated. No need for especially adapted quantification references.
• Additional isotope ratio analysis and careful selection of retention time ranges for detection
of the different formula groups allow detecting and minimising interferences between
sPCAs and mPCAs.
• Number of necessary injections per sample can be reduced.
Disadvantages:
• No lower chlorinated formula groups (Cl 3 and Cl 4 ) detectable.
