Incorporation of flow injection analysis or capillary electrophoresis with resonance Rayleigh scattering detection for inorganic ion analysis

Resonance Rayleigh scattering (RRS) has been explored as a detection (RRSD) technique for capillary electrophoresis (CE) or flow injection analysis (FIA) of inorganic ions. The detection was achieved through a scattering probe of ion-association complex formed from rhodamine B (Rh B) and iodine. The probe scatters strongly at 630 nm when oxidants such as Cr2O72−, MnO4− and ClO− present in a mixed solution of Rh B and iodide. The scattering disappears once iodine is reduced by reductants. Oxidant or reductant species in a sample can thus be detected by positive or negative RRS signal. To verify the RRSD, FIA-RRSD was first constructed and continuous measurement of testing samples containing Cr2O72−, MnO4− and/or ClO− was performed. The detection limits reached a level of decade nM and a linear range was found between peak height and concentration at the range of 0.255–2.04 μM for Cr2O72−, 0.158–3.16 μM for MnO4−, and 1.18–9.43 μM for ClO−, with linear regression coefficients of all above 0.99. The run-to-run relative standard deviation of peak height was less than 3% (n = 6). CE-RRSD was then set up and studied, using a capillary of 75 μm i.d. × 33 cm filled with a running buffer of 50 mM citrate and 25 mM Tris (pH 3.32) and worked under −12 kV at room temperature. The CE eluent was at-line conducted into a stream of rhodamine B and iodine flowing inner a wide tube by plugging the capillary outlet into the wide tube. Different mixtures prepared from Cr2O72−, MnO4− and ClO− were successfully separated and detected by the CE-RRSD.