Standard additions in flow injection analysis based on merging zones and gradient exploitation: application to copper determination in spirits

A novel strategy for implementing the standard addition method in flow analysis is described. It requires only one standard solution and provides several addition levels using a single injection. Data acquisition and treatment are performed by means of a microcomputer running a software in C-language. A mathematical model to account for the changes in sample matrix due to differences in dispersion associated with the different addition levels is derived. It corrects also deviations related to the asymmetry of the merging zones process. Model systems are critically examined for potassium determination in synthetic samples by flame photometry, to which ethanol or glycerol are added to promote different matrix effects. As application, the determination of copper in spirits by flame atomic absorption spectrometry was selected. The proposed system handles about 60 samples per hour and yields precise results (R.S.D. usually < 5%) regardless of the ethanol content of the assayed samples. Comparison with an alternative procedure involving sample evaporation and manual water dilution revealed systematic deviations usually < 3%.