Gas Chromatography - Tandem Techniques - Examples of GC/MS Spectrometry Applications > Determination of Pesticides in Biological Matrixes > Page 83


Figure 67. Chromatograms and MS/MS Spectra for Chlorothalonil and Procymidone at Concentrations of 0.21 and 145 mg per kilo Respectvely.


The molecular weight of the main fragments obtained from chlorothalonil are 266, 268 and 264 and those from procymidone are 283,and 285. It is seen from figure 67 that these fragments are clearly and unambiguously observed and that concentrations of 0.1 mg per kilo chlorothalonil could easily be determined. The advantages of combining the gas chromatograph with the mass spectrometer for environmental studies are clearly demonstrated. The polycyclic aromatic hydrocarbons (PAHÕs) are also important pollutants that are readily spread through the environment from various industrial sources and consequently need to be monitored. The high sensitivity and high selectivity of the GC/MS system makes it an obvious choice for the preferred method of analysis of such materials. The PAHÕs are now widespread in the environment and have both carcinogenic and mutagenic activity. The US Environmental Protection Agency and the European Community have selected 16 PAHÕs for their ÒPriority Pollutant ListÓ. Studies have shown, however, that those PAHÕs that have a molecular weight of 300 or more (the high molecular weigh PAHÕs , i.e., > 6 aromatic rings or >24 carbon atoms) give positive mutagenic responses when isolated from environmental and combustion related samples. It was also found that the PAHÕs having molecular weights of 300 or greater accounted for over 50% of the total carcinogenic activity.