Gemini surfactant applied to the heparin assay at the nanogram level by resonance Rayleigh scattering method.

We present here a resonance Rayleigh scattering (RRS) method for the determination of heparin at the nanogram level using gemini surfactant (dodecyl polyoxyethylene ether biquaternary ammonium salt, DPBAS). It was found that DPBAS could react with anionic heparin to form an ion-association complex, which induced the enhancement of RRS intensity and the appearance of a new RRS spectrum in Britton-Robinson buffer (pH 5.5). The RRS spectral characteristics of the heparin-DPBAS system, the optimum conditions of the reaction, and the influencing factors have been investigated. Under the optimum conditions, the enhanced RRS intensity (ΔI(RRS)) was proportional to the concentration of heparin in the range of 0.05-0.6μg/mL. The method has high sensitivity, and the detection limit for heparin is 4.3ng/mL. The proposed method has been successfully applied for the determination of heparin in pharmaceutical samples. Furthermore, the mechanism of the interaction between heparin and DPBAS was explored using RRS and conductivity methods, indicating that the gemini surfactant reacting with heparin mainly exists in the form of micellar-type aggregates. A model of the reaction between heparin and DPBAS molecules has been proposed.