Comparative qualitative analysis of nonylphenol isomers by gas chromatography-mass spectrometry combined with chemometric resolution. 
The relationship between nonylphenol (NP) isomers' structures and their estrogenic potencies has been evaluated previously.  However, due to their similarities in both chemical and physical properties, complete separation and identification remain strikingly difficult.  In the present study, gas chromatography-mass spectrometry (GC-MS) is employed to separate commercial NP isomers.  Both extracted ion chromatograms (EIC) based on selected ions known to be definitive for the suite of isomers, and the heuristic evolving latent projection (HELP) chemometric resolution method have been applied for the analysis and identification of the NP isomers.  This method corrected the wrong identification of one isomer which was suspected based on the EIC data, and also was able to be applied for the determination of an additional isomer with low abundance.  Overall, 15 NP isomers have been proposed by the HELP interpretation method.  Pure component chromatograms and mass spectra have been extracted with the aid of chemometric resolution.  The applicability of the commercial deconvolution software package automated mass spectral deconvolution and identification system (AMDIS) has also been tested against the HELP method for comparative presentation of pure component mass spectra.