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 pro vides several addition levels using a single injection. Data acquisiti on and treatment are performed by means of a microcomputer running a s oftware 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 rel ated to the asymmetry of the merging zones process. Model systems are critically examined for potassium determination in synthetic samples b y 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 p roposed system handles about 60 samples per hour and yields precise re sults (R.S.D. usually < 5%) regardless of the ethanol content of the a ssayed samples. Comparison with an alternative procedure involving sam ple evaporation and manual water dilution revealed systematic deviatio ns usually < 3%.