On-line solid phase extraction preconcentration of ultratrace amounts of cobalt and nickel in soil and human hair samples for determination by flow injection flame AAS

A flow injection on-line solid phase extraction (SPE) preconcentration system, coupled to a flame atomic absorption spectrometer (FAAS), was developed for the determination of cobalt and nickel at the mug/L levels. Cobalt and nickel were complexed with 2,3-dihydroxy naphthalene (DHN) in the pH range of 2.0-8.0 in the flow injection system and adsorbed onto a C-18-bonded silica gel microcolumn. The preconcentrated metal-DHN complexes were eluted with acidified methanol (pH similar to2). The eluent was injected directly into the nebulizer of a FAAS for measurement. The enrichment factors were 725 and 600 for cobalt and nickel, respectively, with a 1-min preconcentration time and a sample throughput of 30/h. The detection limits, corresponding to three times the standard deviation of the blank, were found to be 0.1 mug/L with a precision of 2.5 and 2.6% (RSD) for five successive determinations of 10 mug/L of Co and Ni, respectively. No significant interference was observed from neutral electrolytes, Fe, Zn, and Cu. In addition to testing the accuracy of the developed procedure for the analysis of nickel soil reference material (IAEA, Soil-7), the method was also applied successfully to the determination of Ni in soil and Ni and Co in human hair samples.