Cationic Surfactant Analysis with Good Laboratory Practice and Waste Management

The objectives of this research are to (a) demonstrate how to select an organic solvent (such as 1,1,1-trichloroethane) for spectrophotometric determination of cationic surfactant in water and wastewater; (b) investigate and recommend possible better organic solvents for surfactant analysis; and (c) introduce good laboratory practice for personal protection, laboratory protection, and hazardous waste management. Specifically, this research involves selection of alternate less toxic and greener organic solvent for use in a methyl orange method for colorimetric determination of cationic surfactants in the 0.2 to 2.0 mg/L range. The principles, steps and management of the methyl orange method include the following (a) complexation of cationic surfactant with methyl orange at acidic pH condition forming a methyl orange-surfactant complex; (b) organic solvent extraction; (c) water-solvent phase separation; (d) spectrophotometric measurement; and (e) good laboratory practice and laboratory hazardous waste management. Initially, the water sample to be analyzed is treated with 50 mL of organic solvent and an excess amount of methyl orange dye reagent in the presence of a pH-3 buffered solution. The methyl orange reagent reacts with the cationic surfactant forming an organic solvent-soluble complex (i.e., a methyl orange-surfactant complex). The complex is dissolved in the organic solvent phase by rapidly shaking the separatory funnel for a sufficient short period of time. Since the organic solvent is heavier than water, the organic solvent phase can be separated from the water phase simply by gravity separation. The intensity of yellow color in the organic solvent layer is directly proportional to the methyl orange-surfactant complex concentration. Thus, the intensity of the yellow color can be subsequently measured by the use of a spectrophotometer (light path = 10 cm). The absorbance curves for the treated surfactant (cetyldimethylbenzylammonium chloride; or any target cationic surfactant in an industrial water) show an absorbance maximum of 415 nm. The preliminarily selected organic solvent in this initial demonstration research is 1,1,1-trichloroethane, which is less toxic than the commonly used chloroform. Chloroform is one type of toxic trihalomethanes (THM). The even greener organic solvents recommended by the authors for further replacing 1,1,1-trichloroethane are D-limonene (C10H16) and alkyl bromide. The readers are encouraged to investigate the feasibility of using even better, greener organic solvents for various analytical methods involving the use organic solvents. Laboratory personal protection, laboratory protection, and waste management are introduced in detail