RESUMO

The endocrine disrupting chemicals bisphenol A (BPA) and 4-nonylphenol (NP) were simultaneously quantified through third-order/four-way calibration. Excitation-emission fluorescence matrix-kinetic (EEFM-K) third-order data were generated by measuring the EEFMs of these priority xenoestrogens as a function of reaction time during their Fenton degradation. Third-order/four-way calibration notably improves the sensitivity of the method and provides the required selectivity for quantifying analytes with critically overlapped fluorescence signals. In fact, collinearity between BPA and NP emission spectra prevented their quantification using EEFM second-order data and three-way PARAFAC (parallel factor analysis); however, the addition of a third instrumental mode allowed the correct chemometric modeling with four-way PARAFAC. In this way, the compliance of Kruskal's theorem extended to higher-order data was verified. The method was applied for the determination of the analytes in samples of different plastic materials, which are in contact with food and/or beverages. In these cases, where unmodelled constituents are present, good results for BPA were achieved with four-way PARAFAC, but the predictions for NP using this model were deficient. A better predictive capability for NP in real samples was achieved when either U-PLS/RTL (unfolded partial least-squares combined with residual trilinearization) or MCR-ALS (multivariate curve resolution with alternating least-squares) was applied for data processing, demonstrating the power of these latter models for the resolution of more complex systems.

Assuntos

RESUMO

For the first time, a simple and environmentally friendly third-order/four-way calibration was applied for the simultaneous determination of five heavy-polycyclic aromatic hydrocarbons (PAHs) in interfering environments. The kinetic evolution of the Fenton degradation of benzo[a]pyrene, dibenz[a,h]anthracene, benzo[b]fluoranthene, benzo[k]fluoranthene and benz[a]anthracene was followed by recording full excitation-emission fluorescence matrices (EEFMs) of the samples at different reaction times, obtaining third-order EEFM-kinetic (EEFM-K) data. The sensitivity of the method was increased by carrying out the reaction in the presence of methyl-ß-cyclodextrin. The four-way parallel factor (PARAFAC) algorithm, which was used for data processing, exploits the second-order advantage, allowing analyte concentrations to be estimated even in the presence of an uncalibrated fluorescent background. The clear superiority of the applied approach in comparison with second-order/three-way calibration performed with unreacting EEFMs is demonstrated, using two sets of samples with foreign compounds with particular spectral profiles. In one of the latter sets, the existence of a third-order advantage was explored and discussed. The feasibility to directly determine parts-per-trillion concentration levels of PAHs after a very simple solid-phase extraction with C18 membranes is established with natural water samples containing uncalibrated constituents.