Determination of Vanadium in Alkaline Leachates of Vanadium Slags Using High-Resolution Continuum Source Graphite Atomic Absorption Spectrometry (HR-CS GFAAS) Part I: The Influence of Sample Matrix on the Quality of Graphite Atomizer

Interactions between alkaline solutions and the surface of pyrolytically coated graphite tubes (PCGTs) with/without a platform for determination of vanadium using high-resolution continuum source graphite furnace atomic absorption spectrometry (HR CS GFAAS) are discussed. Changes on the surface of tubes, lifetime of tubes, and formation of memory effect in the determination of vanadium in alkaline solutions (NaOH, Na2CO3, and real alkaline slag leachates) were investigated. Based on the results obtained, it is possible to state that HR CS GFAAS determination of vanadium content in alkaline solutions reveals that PCGTs with a platform are more susceptible than those without a platform to the formation of deposits and degradation of the platform surface, especially after the application of hydroxide environments. More marked and faster formation of deposits leads to shortening of the analytical lifetime of PCGTs with a platform (approx. 70 atomization/analytical cycles (ACs)) compared to PCGTs without a platform (approx. 290 ACs). The mechanical life of both types of tubes is comparable (approx. 500 ACs). Deposits formed on the internal surface of PCGTs can be removed in the presence of a carbonate environment and higher temperatures. Damage to the PCGT surface leads to the formation of scaled shapes and cavities, which can result in decreased absorbance due to losses of vanadium in the cavities (negative measurement error), or in increased absorbance by washing out of vanadium from the cavities (positive measurement error, and formation of memory effect). It was found that more frequent cleaning of PCGTs by performing ACs in an environment of 4 mol L−1 HNO3 can eliminate these unfavourable phenomena. Our results have shown that in the case of samples analysed with different sample environments (acidic vs. alkaline), the surface material of the tube/platform wears out more quickly, and therefore it is necessary to include a cleaning stage after changing the nature of the environment.