Analytical curve or standard addition method: how to elect and design--a strategy applied to copper determination in...

In most instrumental analysis, the analyte concentration is usually obtained the by Analytical Curve Method (ACM) or Standard Addition Method (SAM). Thus, it is important for the analyst to select the most appropriate method, to seek the best conditions of analysis, and to provide parameters of analytical performance. A strategy to do so is proposed in this paper in conjunction with MATLAB software to implement it. The proposed strategy was applied to copper determination by atomic absorption spectrometry in Brazilian sugarcane spirits termed 'Cachaça' and SAM was chosen as the most appropriate method. To select the best experimental design for SAM, the influence of some factors, such as the number of standard additions and concentration levels, the location of the levels and the average concentration of the standard additions were demonstrated. The design with six standard additions, four concentration levels located near the inferior and superior levels and the average concentration of the standard additions closer to zero yielded SAM with an adequate compromise between precision, cost and time of analysis. The uniform distribution of concentration levels, usually used in routine analysis, is not a good design regarding precision. On the other hand, it is adequate when the linear range is unknown. Generally, the proposed strategy can be applied to different instrumental techniques and samples, which aim to improve their analytical performance.