LC Separation and Indirect Detection of Analyte Anions Using Ru(phen)3 (CIO4)2 as a Mobile-Phase Additive: Wavelength Selection and Application

The application of the intense ultraviolet π—π* transition absorption band at 261 nm for indirect detection of analyte anions using Ru(phen)3(CIO4)2 as a mobile phase additive is studied. The results are compared with those obtained using the conventional absorption band at 447 nm for the d—π* charge transfer transition. Variation of the concentration of Ru(phen)3(CIO4)2 is shown to influence the sensitivity of the methods with absorption at the two wavelengths. Use of a low Ru complex concentration is found to reduce noise and increase the gain in absorbance per mole RuL32+ liberated, resulting in an increase in the signal-to-noise ratio. Using 0.01mM Ru(phen)3(CIO4)2 and 261 nm as the absorption wavelength, the detection limits of the method as measured by 2 times the noise level for F-, Cl-, Br-, and NO3- are 5 ppb (0.1 ng), 5 ppb (0.1 ng), 10 ppb (0.2 ng), and 10 ppb (0.2 ng), respectively.