ES&T LETTERS Guidelines Dear Sir: In response to your March 1982 editorial, "Guidelines for G C / M S identification," we submit the following comments and recommendations. We concur that improved quality control is needed for journal article statements about organic compound identifications. Frequently, authors list organic compounds as "identified" in environmental samples but fail to provide adequate supporting evidence. The problem, however, is not restricted to identifications based on gas chromatography/mass spectrometry ( G C / M S ) . In fact, the widespread application of G C / M S to environmental samples during the past few years has significantly improved the reliability of reported pollutant identifications, many of which previously were based on much less evidence than is routinely acquired now with G C / M S procedures. Establishing arbitrary quality descriptors (such as tentative, confident, and confirmed) for identifications based on G C / M S data does not adequately address the quality control problem; M S is only one analytical technique used to provide evidence for structural assignments. Quality control is also desirable for identifications based on G C with conventional detectors, high-performance liquid chromatography, G C / F o u r i e r transform infrared spectrometry, and other types of M S data. The level of confidence associated with an identification varies with several factors, only one of which is the type of M S data obtained. M S data in addition to an electron ionization (EI) spectrum do not always provide a higher level of confidence than EI data alone. For example, the proposed second-level quality category, "confident structure assignment," assumes that a chemical ionization (CI) spectrum or accurate mass measurement ( H R M S ) will always provide additional structural information. In the case of polycyclic aromatic hydrocarbons having the same empirical formula, neither C I M S nor H R M S would validate a tentative identification based on electron ionization M S data. We suggest that the best approach to solving the problem is through an improved peer review system. Re-
viewers should be specifically requested to evaluate critically all of the evidence presented to support structural assignments and, for each manuscript, to determine if the author's statements are appropriate. Journal editors should be charged with the responsibility of selecting reviewers competent in the areas of analytical chemistry pertinent to a particular manuscript. When a qualified reviewer thinks that reported identifications are not accompanied by sufficient supporting data, the author would have the option of providing more data or revising statements to describe more accurately the probability of valid identification. The primary concern is not adjective selection but inclusion of supporting data. If authors are forced to be more careful to document statements about identifications—or not be published—journal article quality will improve. The reader, both now and in the future, must judge the probability of valid identifications, considering the evidence provided in the light of contemporary technology and practice. Setting arbitrary adjective descriptors of confidence now will contribute to confusion in the future, because current criteria will undoubtedly require modification as analytical technology evolves and new techniques are developed. We hope these comments will be useful and will at least promote further dialogue on this subject. Ann Alford-Stevens, research chemist William L. Budde, chief Advanced Instrumentation Section U.S. EPA Environmental Monitoring and Support Laboratory Cincinnati, Ohio 45268 G C / M S identification Dear Sir: Your proposed criteria for an identification by G C / M S are good. In essence, the suggestion is that the electron impact and chemical ionization mass spectra and the G C retention time agree with the authentic compound. My only quibble is that the chemical ionization spectrum frequently is not available, either because of instrumental difficulties or, more importantly, the compound simply does not ionize under simple chemical
ionization conditions. Therefore, the insertion of the phrase "where possible" preceding chemical ionization would be a useful caveat. I think it is also important to stress that an identification by G C / M S should be put in the context of the problem at hand. Is the identification plausible for the situation in which the compound was found? The classic example of this kind of problem is the identification of azulene (an isomer of naphthalene) by the EPA in several drinking water samples. Because of the similarity of the mass spectra and gas chromatographic retention times of azulene and naphthalene, there is no reason to suspect the identification is in error. However, we should ask ourselves: Is the presence of azulene plausible and reasonable in drinking water? Is the absence of naphthalene plausible and reasonable in drinking water? The answer is " n o , " and we become suspicious of this identification. Therefore, I suggest the addition of such considerations of plausibility and reasonableness to the list of G C / M S identification criteria. Ronald A. Hites, Professor Indiana University Bloomington, Ind. 47405
More on G C / M S identification Dear Sir: I have reexamined your editorial statement on G C / M S (ES&T, Vol. 16, No. 3, 1982, p. 143A) after our conversation in Miami Beach, and I want to document my comments regarding your proposed policy. I fully agree with the need for better documentation of criteria used by an investigator to assign structure to a compound found in an environmental sample. To simply state "confirmed by G C / M S " is far from enough. To this point I support the thrust of your editorial. I do not believe, however, that ES&T should attempt to "cast in bronze" (or concrete) standardized adjective descriptions of degree of confidence of structural assignments. I reach this conclusion mainly for the following reasons: • G C / M S is a powerful tool but not unique in its ability to provide structural information. Will the use of the Environ. Sci. Technol., Vol. 16, No. 11, 1982
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