Determination of ppb-level phenol index using in-syringe dispersive liquid-liquid microextraction and liquid waveguide capillary cell spectrophotometry

We report on an in-syringe dispersive liquid-liquid microextraction (DLLME) technique and its application to the determination of the total phenol index in natural waters. Xylene was used as extraction solvent in combination with a mixture of acetonitrile and n-propanol as dispersion solvents. The analytical procedure consists of mixing the sample with buffer, reacting it with 4-aminoantipyrine and potassium hexacyanoferrate, DLLME, phase separation, and index quantification and was automated using the multisyringe flow injection analysis technique and takes 200 s only. DLLME was accomplished by aspiration of the mixture of extraction and dispersion solvents followed by the aqueous phases into the syringe at a high flow rate. Phase separation occurs due to aggregation of the floating extractant droplets (with their lower specific density) at the head of the syringe. The extractant containing the chromogenic reaction product is then pushed into an optical waveguide capillary cell and spectrophotometrically detected at 500 nm. Figures of merits include a low limit of detection (0.9 ppb), a preconcentration factor of 20, a linear dynamic range up to 140 ppb, and a general standard deviation of 3.1 %. The method enabled the concentration of phenols in well water samples to be determined with a mean recovery of 101 %.