Strategies and Techniques for Identifying Unknown Compounds in Environmental Samples

There are approximately 100,000 industrial and commercial chemicals used currently. Many of these compounds and their degradation products find their way into the environment, either through fugitive emission or intentional release, e.g. pesticides. In some cases their release resulted in extensive environmental damage, an example being polychlorinated biphenyls (PCBs). In order to meet the low levels required for the protection of the environment and human health, highly sensitive and selective targeted techniques are required. Mass spectrometry, coupled with a wide range of ionization and chromatographic interfaces, has become the most widely used technique for the quantitative and qualitative analysis of environmental pollutants. Mass spectral libraries contain electron ionization mass spectra of over 200,000 compounds, which are produced using pure standards under ideal conditions. For many environmental samples, however, obtaining clean spectra is a challenge. Also, as is often the case for degradation products and impurities, library spectra may not be available. Advanced (multidimensional) chromatographic separations, in combination with high resolution mass measurements, provide a wealth of information. This chapter outlines various strategies and techniques that can be employed for the identification of unknown compounds in complex environmental samples.