Abstract
A new method for simple colorimetric determination of alkylbenzenesulfonate (ABS) has been proposed using polyvinyl chloride as adsorption material of Crystal Violet (CV) and ABS complex. A small amount of ABS was selectively adsorbed on a polyvinyl chloride sheet in the presence of excess CV. The color intensity of the sheet adsorbing the CV-ABS complex was proportional to the ABS concentration of the aqueous solution, and thus the concentration of ABS could be determined visually or spectrophotometrically. The absorption maximum wavelength of the sheet was 596 nm, and color was very stable. When the sheet was immersed in 100 ml of ABS aqueous solution containing 0.001% CV at pH 2 for 15 minutes, the detection limit of ABS was found to be 0.2 ppm by the visual method. The applicable concentration range of ABS was 0.2 to 10 ppm. The color intensity increased gradually with immersing time; the absorbance came to above 2 when the sheet was immersed in 100 ml of 5 ppm ABS solution for 1 day. It was observed that the polyvinyl chloride containing plasiticizer, such as dioctyl phthalate or tricresylphosphate, adsorbed the CV-ABS complex, and that the color intensified with the increasing concentration of plasticizer in the polyvinyl chloride. Polyvinyl chloride not containing plasticizer slightly adsorbed the colored complex or not at all.
The recommended analytical procedure is as follows. Add 1 ml of 1 N sulfuric acid and 2.5 ml of 0.04% CV solution to the neutralized sample solution which containes less than 1 mg of ABS, and dilute to 100 ml with water. Immerse a plasticized polyvinyl chloride sheet (for example, 15×35×1 mm) in the solution for 15 minutes. Take up the sheet from the solution, wash it with water, and wipe the sheet to remove the water. Visually compare the color intensity of the sheet with the standard series previously prepared, or spectrophotometrically measure the absorbance at 596 nm. One hundred ppm of the other anions such as chloride, bromide, iodide, nitrate and stealate, colored very slightly the sheet by the proposed method.
