A PVC sensing phase for determination of BTEX in water employing mid-infrared spectroscopy

The evaluation of PVC films, cast with 2-(2-hydroxy-5-tert-octylphenyl)benzotriazol (Tinuvin) as stabiliser (0.3%) and di-2-ethylhexyl phthalate (DOP) as plasticiser (25 or 40%), for use as sensing phases for benzene, toluene, ethylbenzene and xylene (BTEX) determinations, based on transmittance measurements in the mid-infrared (MIR) region, is described. Measurements were carried out by inserting a PVC sensing phase into a vial, which was then completely filled with the hydrocarbon sample solution. Afterwards, the sensing phase was removed from the vial and placed in the optical path of a spectrophotometer for acquiring absorbance spectra from 12,800 to 650 cm−1. Kinetic measurements showed that the films reached saturation within 180 min for all BTEX compounds. Analytical curves were constructed for BTEX compounds in the 0–80 mg L−1 concentration range, showing, respectively, detection limits and sensitivities (expressed as the slope of the analytical curves) of 5.0 mg L−1 and 2.6 × 10−5 L mg−1 for benzene (measured at 688 cm−1), 6.9 mg L−1 and 3.6 × 10−5 L mg−1 for toluene (at 728 cm−1), 9.0 mg L−1 and 4.7 × 10−5 L mg−1 for ethylbenzene (at 695 cm−1), and 4.0 mg L−1 and 3.7 × 10−5 L mg−1 for xylene (at 778 cm−1), when PVC film with 25% plasticiser was employed. The sensitivity was increased when 40% of plasticiser was used in the film preparation. These results demonstrate the feasibility of using transmittance measurements in the mid-infrared region for determining BTEX compounds in water, after their extraction by a PVC film.