Simultaneous determination of BTX and total hydrocarbons in water employing near infrared spectroscopy and multivariate calibration

A method for the simultaneous determination of benzene, toluene and xylenes (BTX) in water based on the use of a silicone sensing phase, detection by near infrared spectroscopy and multivariate calibration is described. A Doehlert design was employed to define the calibration and external validation sets, which were prepared in the concentration ranges of 2.0–30 mg L−1 for benzene, 4.0–40 mg L−1 for toluene and 1.0–15 mg L−1 for xylenes; these ranges were selected after evaluation of the concentration of these compounds in a water sample contaminated by gasoline. The determinations were performed by inserting a polydimethylsiloxane (PDMS) rod (3.2 mm diameter and 5.0 mm long) into a flask containing the aqueous BTX solution (without headspace), made 3.0 mol L−1 with sodium chloride in order to improve the extraction of the hydrocarbons by the polymer. After extraction, the cylinder was placed in a home-made cell for absorbance measurements from 800 to 2500 nm. The calibration models were constructed using Partial Least Square (PLS) regression and Multiple Linear Regression (MLR), with variables selected by the Successive Projection Algorithm (SPA). PLS models provided relative errors of prediction of 10.9%, 13.3%, 21.9% and 9.6% for benzene, toluene, xylenes and total hydrocarbons, respectively. These values can be considered acceptable for the concentration range studied, indicating that the proposed method can be useful for simultaneous determination of aromatic compounds in water employing NIR.