Spectrophotometric determination of trace ionic and non-ionic surfactants based on a collection on a membrane filter as the ion associate of the surfactant with Erythrosine B

Abstract

The spectrophotometric method for the determination of trace surfactants with Erythrosine B (EB) based on the aqueous reaction and the collection on a membrane filter by filtration was studied. Cationic surfactants (CS +), such as a quaternary ammonium ion, and polyoxyethylene non-ionic surfactants (NS) in the presence of potassium ion, containing a long-chain alkyl group associate with EB buffered at pH 5.5. CS + associates with anionic surfactants (AS −). For the determination of CS +, four methods were employed: the collection of the ion associate of CS + with EB on a mixed cellulose ester (MCE) or PTFE membrane filter, the collection of the ion associate of CS + with AS − on a PTFE membrane filter followed by the ion exchange of AS − with EB, and the first collection of CS + followed by the second collection of EB on a PTFE membrane filter. For the determination of AS −, the collection of the ion associate of AS − with CS + on a PTFE membrane filter followed by the ion exchange of AS − with EB was done. For the determination of NS, the ion associate of NS with EB was collected on a MCE membrane filter. The MCE membrane filter with the analyte was dissolved in methyl cellosolve. The analyte on the PTFE membrane filter was eluted with ethanol. The CS + up to 5×10 −7 M can be determined by the absorbance at 542 nm of the methyl cellosolve solution or the absorbance at 535 nm of the ethanol solution. The AS − up to 5×10 −7 M can be determined by the absorbance at 536 nm of the ethanol solution. The NS up to 2.53×10 −6 M can be determined by the absorbance at 537 nm of the methyl cellosolve solution. This is the sensitive method for the determination of 10 −8 to 10 −7 M order of ionic surfactants and 10 −7 to 10 −6 M order of NS without toxic organic solvents.