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using CH4/CH2CI2, where only deviations of 1-2.5 % were observed (Zencak et al, 
2003). 
• However, CH4/CH2CI2-NICI contaminates the ion source rather quickly and was 
therefore only applied to a few selected biota samples. Figure 5 clearly shows the 
presence of considerable amounts of Cl3_4 compounds (Zencak et al, 2003). 
• Sediments contained a rather high background and partly low concentration, so 
that determination by ECNI was hampered with the Hewlett Packard mass 
spectrometer. Therefore, all analysis was carried out by CH4/CH2CI2-NICI until new 
ECNI instrumentation allowed achieving lower detection limits and higher 
selectivity in 2003.