There is a general consensus that supports the need for standardized reporting of metadata or information describing large-scale metabolomics and other functional genomics data sets. Reporting of standard metadata provides a biological and empirical context for the data, facilitates experimental replication, and enables the reinterrogation and comparison of data by others. Accordingly, the Metabolomics Standards Initiative is building a general consensus concerning the minimum reporting standards for metabolomics experiments of which the Chemical Analysis Working Group (CAWG) is a member of this community effort. This article proposes the minimum reporting standards related to the chemical analysis aspects of metabolomics experiments including: sample preparation, experimental analysis, quality control, metabolite identification, and data pre-processing. These minimum standards currently focus mostly upon mass spectrometry and nuclear magnetic resonance spectroscopy due to the popularity of these techniques in metabolomics. However, additional input concerning other techniques is welcomed and can be provided via the CAWG on-line discussion forum at

Volatile organic compounds play a central role in the processes that generate both urban photochemical smog and tropospheric ozone. For successful and accurate prediction of these pollution episodes, identification of the dominant reactive species within the volatile organic carbon pool is needed. At present, lack of resolution inherent in single-column chromatographic analysis limits such a detailed chemical characterization of the complex urban atmosphere. Here we present an improved method of peak deconvolution from double-column (orthogonal) gas chromatography. This has enabled us to isolate and classify more than 500 chemical species of volatile organic compounds in urban air, including over 100 multi-substituted monoaromatic and volatile oxygenated hydrocarbons. We suggest that previous assessments of reactive carbon species may therefore have underestimated the contribution made by volatile organic compounds to urban pollution, particularly for compounds with more than six carbon atoms. Incorporating these species in predictive models should greatly improve our understanding of photochemical ozone yields and the formation of harmful secondary organic aerosols.

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Comprehensive two-dimensional chromatography employs a serially coupled two-column arrangement where effluent from the first column is collected or sampled and then introduced to the second column according to a chosen modulation period. This is effected by use of a modulator at or near the column junction. One of the considerations in applying the technique is the period of the modulator, which determines the sampling duration of the first column effluent. Here, we propose that the sampling rate can be most effectively described by a new term, called the modulation ratio (MR). This is defined as the ratio of 4 times the first column peak standard deviation (4sigma) divided by the modulation period (PM) or 1.6985 times the half-height width of the peak (wh): MR = 4sigma/PM = wb/PM = (wh x 1.6985)/PM. The 4sigma value is more commonly recognized as the peak base width (wb). The use of 4sigma as the numerator is preferred to simply sigma because when the PM value used for an experiment is equal to sigma, then the MR value is calculated to be 4, implying that the primary peak will be modulated approximately 4 times as is normally recommended for a comprehensive multidimensional separation. The less well-defined term of modulation number (NM) has been previously used and proposed as the number of modulations per peak and, therefore, is intended to convey the manner in which the primary column peak is sampled; this is a subjective and not well-characterized value. The use of MR should provide users with a meaningful and strictly defined value when reporting experimental conditions. The utility of MR is demonstrated through a mathematical model of the modulation process for both Gaussian and tailing peaks, supported by an experimental study of the modulation ratio. It is shown that for the analysis of trace compounds where precise quantitative measurements are being made, the experiment should be conducted with an MR of at least 3. Conversely, for semiquantitative methods or the analysis of major components, an MR of approximately 1.5 should suffice.

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