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Since PCAs cannot be resolved gas chromatographic ally even into formula groups, the 
gas chromatographic separation was carried out with short columns and a quick 
temperature programme to shorten analysis time and to increase signal height with a 
corresponding decrease of detection limits. Minimum requirements were maintained 
such as retention time differentiation between short and medium chain PCAs (Reth and 
Oehme, 2004). 
5.3.3.2 Mass spectrometry 
The following mass spectrometric techniques were developed or improved during this 
project: 
• Negative ion chemical ionisation (NICI) with a mixture of CH2CI2/CH4. Chloride 
anions are generated from CH2Cl2-They form exclusively the molecular ion adduct 
[M+Cl]" from PCAs (Zencak et al, 2003). 
• El combined with MS/MS in a ion trap or with a triple quadrupole mass 
spectrometer by selecting fragments common to all PCAs formula groups and to 
fragment them further (Zencak et al, 2004). 
• Minimisation and correction of the influence of the degree of chlorination of 
PCAs in a sample on the overall response factors (Reth et al, 2005). 
• Replacement of HRMS by LRMS and elimination/minimisation of mass overlap 
interferences by a careful retention time range selection and isotope ratio control of 
registered masses (Reth and Oehme, 2004). 
In the following, the newly developed and applied mass spectrometric techniques are 
shortly characterised. Their advantages and disadvantages can be summarised as 
follows: