This paper reported on the analytical precision in flame atomic absorption spectrometry when an internal standard method, in which absorption lines of the analyte and internal standard element were measured sequentially (sequential method), was applied by using a continuum-light source spectrometer. For comparison, our previous paper regarding an internal standard method by measuring them simultaneously (simultaneous method) was also referred to. Relationships between the absorbance and iron concentration and the ranges of their linear calibration were investigated for 23 iron atomic lines (as the internal standard line), so that an optimum iron line could be selected for the internal standardization. The result indicated that the allowable range of the concentration could be predicted from the product of the relative number density and the transition probability of these absorption lines. The sequential method for an internal standard was carried out in the determination of nickel in a steel sample, to correct for any physical interference occurring in a flame and a drift of the signal response in the measurement. In conclusion, the analytical precision in the sequential method was less improved than that in the simultaneous method.
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