Measuring Polycyclic Aromatic Hydrocarbons in Water using the Simultaneous Absorbance and Fluorescence Excitation-Emission Matrix Method: Advantages of Classical Least Squares Regression Over Parallel Factor Analysis

Abstract

Many Polycyclic Aromatic Hydrocarbons (PAHs) are carcinogenic and hence of important environmental concern in drinking water sources. Most USEPA PAHs of concern exhibit high fluorescence quantum yields and sub mg/l to μg/l detection limits in neat solutions. However, drinking water sources commonly contain other natural compounds, including humic and fulvic acids and proteins, in carbon concentrations of several mg/l that exhibit significant interfering absorbance and fluorescence backgrounds in the PAH detection region. We investigated the use of the new simultaneous Absorbance and fluorescence Excitation-Emission Matrix (ABEEM) method to measure PAHs in raw water. The ABEEM method corrects fluorescence inner-filter effects to yield quantitative fluorescence spectral information to be largely independent of component concentrations. We compared Classical Least Squares Regression (CLS) and Parallel Factor Analysis (PARAFAC) in terms of identification and detection limits for the PAHs. The CLS library was calibrated with respect to concentration for the individual EPA PAHs dissolved in deionized organic-carbon free water. The same data set was used calibrate a model using the 3-way PARAFAC technique. Validation of the CLS and PARAFAC models was compared with PAHs added to natural raw water of varying organic carbon concentrations. Identification of individual PAHs and mixtures and detection limits were significantly better with CLS. The evaluation is consistent with the fundamental principles CLS vs. PARAFAC and primarily because CLS can be distinctly calibrated with the individual PAH component spectra. We conclude that the identification and detection limits of the ABEEM and CLS analysis can be significant enough for environmental contamination monitoring in drinking water sources; certainly, as a first screening method before the EPA standard solid-phase extraction and liquid or gas-chromatographic analysis methods.