Multicommutation in flow analysis. Part 4. Computer-assisted splitting for spectrophotometric determination of copper and zinc in plants

An improved splitting process in flow analysis accomplished by means of a computer controlled three-way solenoid valve is proposed. This valve is located at the splitting site, and defines the flow pattern and the portions of the processed sample delivered to each emergent stream. As an application, the simultaneous spectrophotometric determination of copper and zinc in plant digests was selected. The method is based on metal complexation with cyanide, differential kinetics of decomplexation, and reaction with Zincon. The proposed system is very stable and handles 45 samples per hour which corresponds to 0.27 mg Zincon per determination. Precise measurements (r.s.d. = 0.7% and 1.7% for first and second peaks) are obtained within 0.00–1.00 mg 1−1 Cu and 0.00–2.00 mg 1−1 Zn. Detection limits are 0.05 and 0.04 mg l−1 for Cu and Zn. Results are in agreement with standard reference materials.