Effect of plasticizers on a PVC sensing phase for evaluation of water contamination by aromatic hydrocarbons and fuels using infrared spectroscopy

The effects of di-2-ethylhexylsebacate (DOS), di-2-ethylhexylphthalate (DOP) and 2-nitro-phenyl-octylether (NPOE) plasticizers on a PVC sensing phase for evaluation of water contamination by aromatic hydrocarbons and fuels were investigated. The performance of each film was assessed by means of figures of merit obtained from analytical curves constructed in different wavenumbers. A mixture design (simplex centroid) with the BTEX compounds was performed in order to evaluate cross-interferences and interaction effects. For preparation of the sensing phase, a mixture of PVC with 25% of the plasticizer and 0.3% of the stabilizer Tinuvin P (2-2′-hydroxy-5-tert-octylphenyl-benzotriazol) dissolved in THF was used. The results show that NPOE and DOP plasticizers present similar performances, while DOS provides better values of sensitivity and detection limit for all compounds. With the use of DOS the detection limits were 2.4, 0.4, 1.5 and 1.2 mg L−1 for BTEX, respectively. Regarding the study of multi-component interactions, it was observed that benzene and xylenes do not show interferences from the other analytes of the mixture at the wavenumbers of 676 and 1522 cm−1, respectively. Ethylbenzene and toluene undergo spectral interferences and interaction effects in all peaks evaluated, requiring a multivariate calibration for their determination. In the analysis of water contaminated by fuels, a 3-D plot as a function of benzene, toluene and xylenes concentrations as well as the principal component analysis of the spectral data presented well-defined groups for each kind of contamination (gasoline A, gasoline C, diesel and diesel with 2% of biodiesel). These results demonstrate the potential of the proposed method, employing a PVC sensing phase, with transmittance measurements in the mid-infrared, for determination of contamination of waters by aromatic hydrocarbons. In conclusion, PVC films plasticized with DOS can be useful for studies of water contamination based on transmittance measurements in the mid-infrared region, avoiding the drawbacks of ATR methods.