Fluorescence excitation emission matrix (FEEM) spectroscopy was used to evaluate its applicability as a tool to track dissolved organic matter (DOM) in a drinking water treatment plant (DWTP) that incorporates a conventional line (consisting in ozonation and GAC filtration) and a membrane-based line (consisting in ultrafiltration, reverse osmosis and mineralization) working in parallel. Seven sampling points within the different process stages were characterized monthly during 2014. A global Parallel Factor Analysis (PARAFAC) was used to pull out underlying organic fractions from the fluorescence spectra. Accordingly a five components model was selected to describe the system and the pros and cons of the model were discussed by analysis of the residuals. Among the five fluorescent components, those associated to humic-like matter (C1, C3 and C4) showed a similar season variability in the river water feeding the DWTP (which resembled that of UV and TOC), whereas the two components associated to protein-like matter (C2 and C5) exhibited a different behavior. The maximum fluorescence intensity values (Fmax) were used to quantify DOM removals across the plant. Compared to the conventional line, water from the UF/RO membrane-based line showed between 6 and 14 times lower fluorescence intensity signal for the humic-like components and between 1 and 3 for the protein-like components as compared to the conventional line. The differences in DOM composition due to seasonal variations and along the treatment trains point out the suitability of using fluorescence measurements over other parameters such as UV as a monitoring tool to help optimize operation conditions of each treatment stage and improve produced water quality in a DWTP.

A method is proposed for the determination of trace rare earth elements (REEs) in graphite by solid sampling electrothermal vaporization-inductively coupled mass spectrometry (ETV-ICP-MS). The operating parameters of the ETV system such as gas flow-rate, heating program, the use of a modifier gas (Freon R-12) as well as sample mass were evaluated. The determination of REE in graphite samples was performed by directly weighing a solid sample (0.5 to 2.5 mg) on the graphite platform of the ETV system. Calibration was carried out using aqueous standards. According to the results, the presence of the modifier gas (Freon R-12) promoted an enhancement of vaporization for all analytes, besides the reduction of the vaporization temperature (about 500 C lower). The accuracy was evaluated by an analyte recovery experiment and also by comparison of results with those obtained by microwaveassisted extraction (MAE) with further determination of REE by ICP-MS equipped with an ultrasonic nebulizer (USN-ICP-MS). Agreement was observed between the results obtained by ETV-ICP-MS and MAE with USN-ICP-MS analysis for most of the elements. Analyte recovery ranged from 100.3 to 118.7% and the obtained RSDs were always lower than 24%. The limits of detection were at the ng g À1 level and were similar to those obtained by USN-ICP-MS with previous sample preparation by MAE. The proposed method was suitable for direct determination of REE in graphite. In addition, direct analysis of graphite by ETV-ICP-MS avoided the laborious sample preparation step of graphite and the use of concentrated acids for digestion, minimizing interferences in the determination step by ICP-MS.

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Diagram of the flow system and its working pattern.

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