Ascorbic acid as effective chemical modifier for cobalt determination in nickel-based alloys by electrothermal atomic absorption spectrometry with longitudinal Zeeman background correction

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Abstract
The cobalt contents in nickel-based alloys have been determined with longitudinal Zeeman-effect background corrected electrothermal atomic absorption spectrometry. The solid alloy was decomposed with a minimum amount of aqua regia. This is a challenge because interferences from NiCl2 and HCl are expected. Detailed studies on the interferences from the concomitants verify this point. The reduction in the sensitivity is mainly due to the loss of cobalt as cobalt chloride before the atomization step. The effects of five different categories of modifier, namely organic acids, Pd containing modifiers, phosphate-containing modifiers, inorganic nitrates and metal complex reagents, on the analysis of cobalt are evaluated. Ascorbic acid effectively reduces the interferences from nickel chloride and hydrochloric acid. Thus, results with best accuracy are obtained. The cobalt contents determined with ascorbic acid agree closely with the certified values of the certified reference materials of nickel-based alloys. The detection limit for the proposed method is 5.17 pg and linear range for the calibration curve is up to 875 pg.

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