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EDITORIAL Confirmation of structure Research a1 icles in this journal often involve the study of new or rare organic compounds the identity of which is central to the purpose of the paper. For example, the compounds may be by-products of a chemical or biological process or may be identified in a particular environmental setting. Although most authors are aware of the necessity for detailed proof of structure and submit such proof as a routine practice, this is not always the case. Worse still, some reviewers fail to notice the lack of such proof. In the future we will ask reviewers to be more careful on this point and to require appropriate data to indicate proof of structure for all compounds that are used or identified in an investigation. We are also concerned that authors who propose mechanistic chemical pathways should provide evidence that such pathways are actually followed. In these cases, not only should the structure of each compound be thoroughly proven, but authors should also provide data (e.g., time-sequenced data) that show how the proposed path from one compound to another has been determined. Lacking such data, authors should refrain from proposing complex chemical schemes, Confirmation of structure is often made more difficult by the fact that in many environmental studies we are compelled to deal with analyte concentrations that are extremely low. Here isolation of compounds and proof of structure are very demanding, even for the expert. Seldom are we able to isolate an amount of analyte sufficient to obtain elemental composition, boiling or melting point, and so forth, as in classical studies. Isolating enough for NMR studies is often out of the question. There are still a substantial number of investigators who propose identification based on a chromatographic retention time. In such cases, reviewers should be extremely careful to satisfy themselves that the evidence is conclusive. For example, confirma-
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1990 American Chemical Society
tory columns or Standard Methods should be used ant the samples should not be excessively complex. For more confident proof of structure, spectroscopic data are required, and in the environmental field this has usually meant mass spectral data. However, as spectroscopic methods become increasingly sophisticated we are seeing other methods become more and more credible for determining proof of structure. FTIR methods are becoming more routine, and we expect these methods to become even more popular as special libraries increase and instrument costs come down. Full spectrum UV/VIS or fluorescence spectra, especially of HPLC fractions, are also becoming powerful confirmatory methods for some classes of analytes, especially when combined with class separation procedures. Even in the field of environmental mass spectrometry, the monopoly of GUMS is giving way to new methods such as HPLC/MS, dynamic FAB/MS, and others. The editors recognize that each investigation has unique characteristics and that it would be inappropriate for this or any other journal to specify what methods must be used for proof of structure. What is more important is that authors should be required to establish by an appropriate number of confirmatory methods that the correct structure is proposed. The principles of environmental analytical chemistry are now well enough elucidated that, with the help of reviewers and authors, we should be able to maintain the standards of the journal with respect to confirmation of chemical structure.
Environ. Sci. Technol., Vol. 24, No. 3, 1990
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