Spectrophotometric determination of trace amounts of surfactants with Bromochlorophenol Blue after preconcentration on a cellulose powder

A simple method for the spectrophotometric determination of trace surfactants based on a preconcentration technique involving collection on a cellulose powder was developed. A cationic surfactant (CS+), such as quaternary ammonium salts containing a long-chain alkyl group, was collected on a cellulose powder as a 1 : 1 ion associate with a monovalent Bromochlorophenol Blue anion (HBCPB-). For the anionic surfactant (AS(-)), CS+ was added to AS- and similarly the ion associate of excess CS+ with HBCPB- was collected on cellulose powder. After filtration, the cellulose powder with an ion associate, CS+.HBCPB-, was stirred with a small volume of an alkaline solution. The absorbance of divalent BCPB2- in the solution after centrifuging was measured at 590 nm. The absorbance at 590 nm increased and decreased with increasing the amount of CS+ and AS-, respectively. A calibration graph based on this principle shows linearity up to 5 X 10(-7) M of CS+ and AS(-). The proposed method is simple and rapid, and there is no use of toxic organic solvents.