Microextraction separation, preconcentration and spectrophotometric determination of sodium dodecyl sulfate as an ion associate with quinaldine red

Abstract

The optimal conditions for the microextraction separation, preconcentration and spectrophotometric determination of sodium dodecyl sulfate (SDS) as an its ion associate (IA) with Quinaldine Red (QR) have been studied. Was tested a large number of organic solvents as extractants. Aliphatic hydrocarbons (hexane) extracted IA considerably weaker than, halogen and nitro derivatives of hydrocarbons (chlorobenzene, bromobenzene, nitrobenzene, chloroform, dichloroethane), extracted with IA and the simple salt of the dye. The best solvent found for the extraction of SDS was mixture of carbon tetrachloride with dichloroethane or chloroform that provided 10 to 50 fold concentration of SDS by microvolume of organic phase. The maximum extraction of SDS was achieved in the concentration range of QR 1.0∙10^–4 mol/l of QR after which the optical density does not change practically (excess dye remains in the aqueous phase). The dye of QR is highly stable in an alkaline environment, it can be used for the extraction of SDS in a wide pH range and rely on high selectivity determination. The pH range for maximum extraction of ion associate was 4–12. We found that 50000–100000-fold amounts F^–, Cl^–, Br^–, NO₂^–, HCO₃^–, CH₃COO^–, SO₄^2–, 10000–20000-fold amounts NO₃^–, I^–, HPO₄^2–, B₄O₇^2–, IO₃^–, ClO₃^–, C₂O₄^2–, 300-fold amounts ClO₄^– do not interfere with the determination of SDS. The molar ratio of SDS and QR determined by various spectrophotometric methods (isomolar series, Asmus, equilibrium shift) is 1:1. The limit of detection was 0.04 µg/ml. A new method of extraction-spectrophotometric determination was applied to the determination of anionic surfactants in various wastewater samples.