1979 Volume 25 Issue 5 Pages 271-278
To eliminate interference in the measurement of anion-active surfactants by the Methylene Blue method, an air-stripping technique was studied. 1) The pH of water sample (containing 0.005-1.25 mg as sodium dodecylbenzenesulfonate, DBS) was adjusted to ca. 7, and transferred into the air-stripping apparatus. Thirty ml of 10% (w/v) NaCl was added to the sample and the whole was diluted to 300 ml with distilled water. After addition of 10 ml of methyl isobutyl ketone (MIBK), the sample was aerated at the rate of 0.1 l/min for 10 min at room temperature, and the MIBK layer was taken into a 50-ml beaker. Another 10 ml of MIBK was added to the sample and aerated in the same manner. The MIBK layer was separated and combined with the former in the beaker. After evaporation of MIBK, the residue was dissolved in distilled water on a water bath, and the content of DBS was determined by the Methylene Blue method. The recovery at the concentration of 0.40 mg/l of DBS was above 95% by this method. 2) The recovery of DBS from a solution containing 0.40 mg/l of underground water, river water, or effluent from wastewater treatment plants was 98.6±3.7% (n=20). 3) Interference of coexisting substances on the determination, such as SCN-, S2-, picric acid, etc., was removed by this method. Cation-active surfactants interfered negatively even by this method. Compared to the values obtained without the air-stripping technique, those obtained with the technique were always lower.
