Surfactant-sensitized post-column reaction with xylenol orange for the determination of lanthanides by ion chromatography

The presence of the cationic surfactants cetylpyridinium chloride and hexadecyltrimethylammonium bromide in an alkaline 40% methanol medium was found to enhance sensitivity when xylenol orange is employed as the post-column reaction reagent for the determination of lanthanides by dynamic ion chromatography. Detection of individual lanthanides was carried out at 618 nm after separation by cation-exchange chromatography with gradient elution on a C₁₈ column. The eluent was -hydroxyisobutyric acid-sodium octanesulfonate, pH 3.8. Sensitivity enhancements by factors of three to six, compared with xylenol orange alone, were achieved at a cationic surfactant concentration of 2.4 mM. The calibration response was linear in the 0.05 to 5 μg ml⁻¹ analyte concentration range. Limits of detection below 3 ng were obtained for all the natural lanthanides and lanthanum. No sensitivity enhancement effects were observed with anionic (sodium dodecyl sulfate) and non-ionic (Triton X-100) surfactants under the conditions tested.