Organosilica composite for preconcentration of phenolic compounds from aqueous solutions

A new adsorbent is proposed for the solid-phase extraction of phenol and 1-naphthol from polluted water. The adsorbent (TX-SiO(2)) is an organosilica composite made from a bifunctional immobilized layer comprising a major fraction (91%) of hydrophilic diol groups and minor fraction (9%) of the amphiphilic long-chain nonionic surfactant Triton X-100 (polyoxyethylated isooctylphenol) (TX). Under static conditions phenol was quantitatively extracted onto TX-SiO(2) in the form of a 4-nitrophenylazophenolate ion associate with cetyltrimethylammonium bromide. The capacity of TX-SiO(2) for phenol is 2.4 mg g(-1) with distribution coefficients up to 3.4 x 10(4) mL g(-1); corresponding data for 1-naphthol are 1.5 mg g(-1) and 3 x 10(3) mL g(-1). The distribution coefficient does not change significantly for solution volumes of 0.025-0.5 L and adsorbent mass less than 0.03 g; 1-90 microg analyte can be easily eluted by 1-3 mL acetonitrile with an overall recovery of 98.2% and 78.3% for phenol and 1-naphthol, respectively. Linear correlation between acetonitrile solution absorbance (A(540)) and phenol concentration (C) in water was found according to the equation A(540) = (6 +/- 1) x 10(-2) + (0.9 +/- 0.1) C (micromol L(-1)) with a detection range from 1 x 10(-8) mol L(-1) (0.9 microL g(-1)) to 2 x 10(-7) mol L(-1) (19 microL g(-1)), a limit of quantification of 1 microL g(-1) (preconcentration factor 125), correlation coefficient of 0.936, and relative standard deviation of 2.5%. A solid-phase colorimetric method was developed for quantitative determination of 1-naphthol on adsorbent phase using scanner technology and RGB numerical analysis. The detection limit of 1-naphthol with this method is 6 microL g(-1) while the quantification limit is 20 microL g(-1). A test system was developed for naked eye monitoring of 1-naphthol impurities in water. The proposed test kit allows one to observe changes in the adsorbent color when 1-naphthol concentration in water is 0.08-3.2 mL g(-1).