Flow analysis with accuracy assessment

The concept of accuracy assessment is exploited in flow analysis. The resulting system is based on multi-commutation because multiple sample processing is involved. The manifold includes different quasi-independent methods and permits recovery tests to be performed on every sample. Results are then intrinsically more accurate and additional information on the sample matrix is provided. The feasibility of the approach is demonstrated in the large scale determination of chloride in river water samples presenting high variability in matrix composition and/or in acidity. The spectrophotometric mercury thiocyanate-Fe(III) method and the turbidimetric method based on the precipitation with silver ions are implemented in a single manifold and a 40.00 mg l−1 Cl− intermittent stream is added in-line to each sample for producing recovery data. Analysis of the four recorded analytical signals permits evaluation and eventual compensation of matrix effects. The final result is calculated after considering the results obtained by two different methods, and the eventual correction of matrix effects. The proposed system is very robust, handles 25 samples per hour and yields precise results between 0.50 and 10.0 mg l−1 Cl−. Potentialities and limitations of the approach are discussed.