Abstract
Reactor replacements is proposed as means of realizing sample residence times in flow-injection analysis. As an application, an improved spectrophotometric determining of cobalt and nickel is proposed. The method exploits differences in reaction rates between cobalt and nickel citrate complexes and 4-(2-pyridylazo) resorcinol (PAR). The influence of pH, reagent concentrations, temperature, ionic stregth, flow-rates and masking agent addition were investigated. Selectively was enhanced by adding EDTA plus pyrophosphate and exploiting kinetic discrimanation. The system is very stable and alows the determination of cobalt and nickel up to 5.00 mg 1 −1 with a sampling frequency of 40 h −1. For tool steel samples characterized by low nickel/cobalt concentration ratios, the system can be simplified, allowing kinetic masking of nickel and single cobalt determination. The reagent consumption is 65.3 μg of PAR per determination, and precise results (R.S.D. 1%) in agreement with inductively coupled plasma atomic emission spectrometry at a sampling frequency of 100 h −1.
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