Direct determination of polymyxin B sulfate using resonance Rayleigh scattering and resonance non‐linear scattering methods with hexatungstate

At pH 1.3–1.6, tungstate WO₄^2–, can be converted to hexatungstate W₆O₁₉^2–, which can react with positively charged polymyxin B sulfate (PMB) to result in enhancement of resonance Rayleigh scattering (RRS) and resonance non‐linear scattering, including second order scattering and frequency doubling scattering. Linear relationships can be established between enhanced scattering intensity and PMB concentration. The detection limits (3σ) were 5.5 ng/mL (RRS), 10.1 ng/mL (second order scattering) and 34.6 ng/mL (frequency doubling scattering). The optimum reaction conditions, influencing factors and related analytical properties were tested. The interaction mechanism was investigated via absorption spectrum, circular dichroism spectra and atomic force microscopy imaging. The basis of scattering enhancement is discussed. PMB in eardrops, human serum and urine, were quantified satisfactorily by RRS. Copyright © 2013 John Wiley & Sons, Ltd.