Eriochrome Black T as a post-column reagent for the ion chromatographic determination of rare earths

The use of Eriochrome Black T in an alkaline, 40% methanol solution was fou nd to be appropriate as post-column reagent for the determination of rare e arths by ion chromatography. Detection of individual lanthanides and lantha num was carried out at 512 nm and 650 nm after separation by dynamic cation exchange chromatography with gradient elution on C-18 column and employing a solution containing alpha-hydroxyisobutiric acid/sodium octanesulfonate at pH 3.8 as eluent. The effect of the presence of micelles in the post-col umn reagent was studied. Sensitivities obtained by the addition of the cati onic surfactants cetylpyridinium chloride (CPC) and hexadecyltrimethylammon ium bromide (CTAB) were lower than those measured without surfactant additi on. In some cases, the signal was totally suppressed. No change in sensitiv ity was observed with non-ionic (Triton X-100) or anionic (sodium dodecylsu lphate, SDS) surfactants but a slight improvement in the baseline noise was observed with the SDS. An evaluation of the influence of chemical and oper ational variables on the post column reaction (PCR) reagent was carried out either by spectrophotometric tests or by chromatographic experiments. A co mparison was performed between three PCR reagents: Eriochrome Black T and x ylenol orange in the presence of a cationic surfactant and arsenate III. Ca libration response was linear up to an analyte concentration of 5.0 mu g ml (-1). Absolute detection limits lower than 7 and 17 ng were obtained at the detection wavelengths of 650 nm and 512 nm respectively, for all the natur al lanthanides and lanthanum. (C) 1999 Elsevier Science B.V. All rights res erved.