Determination of Trace Amount of Cobalt in a Steel Sample by Two-dimensional On-line Redox Derivatization Liquid Chromatography

Abstract

A two-dimensional on-line redox derivatization HPLC system was developed where ''heart-cutting'' chromatography, in conjunction with on-line redox derivatizaion, was used to isolate specific analytes in complex matrix samples. Cobalt in a stainless steel sample was used as a model analyte to evaluate the performance of the HPLC system developed. We adopted a small column packed with porous graphitic carbon (PGC) treated with hydrogen peroxide as an oxidation derivatization unit and two C18 silica columns which had adsorbed hexadecyltrimethylammonium ion as the first and second separation columns. After complexation of metal components with ethylenediaminetetraacetate (edta), the sample was directly submitted to the analysis by the HPLC system without any preseparation steps. In the first dimension separation cobalt was eluted as Co(II)-edta and was separated from trivalent metal complexes such as Fe(III) and Cr(III), while it was selectively oxidized to Co(III)-edta in the PGC column and then completely separated from the divalent metal complexes such as Ni(II) on the second column. A successful application of this method to accurate and precise determination of trace amount of cobalt in a stainless steel is demonstrated.

A Brief Overview of Metal Analysis in Alloys and Related Matrices: Some Classical Methods and Modern Spectroscopic Methods

“…Hoffmann et al 111 realizaram, através de otimizações instrumentais, determinações na faixa de concentração de ng L −1 para 23 elementos em ligas metálicas. Na mesma linha, LA-ICP-MS foi empregada para determinações de metais em moedas de Ag, 112 ligas de Fe, 113,114 Zn, 115 Mg, 116 Ni 117 e com vários elementos majoritários (Fe, Cu, Ni, Co e Al). 118 Utilizando a otimização de parâmetros como atmosfera gasosa, comprimento de onda do laser no UV, dimensão e número de pulsos para um arranjo de LIBS-LA-ICP-MS, limites de detecção de 0,2 (Mo), 0,3 (Mn) e 0,1% (Cr e Ni) foram obtidos em ligas de Mg. 119 A grande vantagem desse arranjo é a possibilidade de se realizar simultaneamente um mapeamento qualitativo da composição do material pela técnica de LIBS e também a razão isotópica através de técnica de ICP-MS.…”

On-Line Redox Derivatization Liquid Chromatography for Selective Separation of Fe(II) and Fe(III) Cyanide Complexes Using Porous Graphitic Carbon

“…[2][3][4][5][6][7][8][9][10][11][12][13][14][15] We recently presented an on-line derivatization method for enhancement of separation selectivity of HPLC. [16][17][18] The HPLC system we used consisted of two separation columns and one derivatization unit placed between them. The derivatization reaction, which will change the chemical form of an analyte compound, proceeds in the derivatization unit so that the analyte migrates in its original form on the first column, while in its converted form on the second column.…”

“…We have found that porous graphitic carbon (PGC) displays catalytic redox activity, which can be modified by treating PGC with a solution of a suitable oxidizing or reducing agent. 16,[18][19][20] We thus adopted a small column packed with PGC particles oxidized by hydrogen peroxide as an oxidation derivatization unit and investigated its redox activity and the efficiency of the system for enhancement of separation selectivity using ethylenediaminetetraacetate (EDTA) complexes of some metal ions as model compounds and two C18 silica columns treated with cetyltrimethylammonium ion as separation columns. 16 Co(II)-EDTA was completely oxidized to Co(III)-EDTA by the PGC column, while the other metal-EDTA complexes were eluted as their original oxidation states throughout the system.…”

“…We applied the on-line derivatization HPLC for the determination of cobalt in a steel sample and demonstrated that trace amounts of cobalt can be determined accurately and precisely by this method without any interference from the matrix metal components. 16,18 However, it has not yet been demonstrated whether or not the PGC exerts the redox activity on metal complexes other than the cobalt polyaminocarboxylates. The redox potential of the PGC ranges approximately from -0.2 to 0.5 V vs. Ag/AgCl reference electrode.…”