A new sample-injection/sample-dilution system for the flow-injection analytical technique Original Research Article

A new sample-injection/sample-dilution system for the flow-injection analytical technique is proposed. The system is based on two variable-speed computer-controlled peristaltic pumps and a specially designed commutator located at the merging point. One of the pumps delivers a sample and the other a carrier solution. The pumps are run in such a way that the total flow rate after the merging point remains permanently constant. The volume of the injected sample is determined by the time the sample delivering pump is on, whilst the dilution of the sample is determined by relative flow rates of sample and carrier solutions. Two additional possibilities are offered by the proposed system. Firstly, the volume of the injected sample plug can be varied in a simple way, and secondly, for the first time, the injection of a sample plug having an exactly predetermined concentration profile for the measured analyte at the merging point can be carried out. By introducing a third pump delivering a standard solution of the measured species, the system is able to perform a quantitative determination of an analyte, either by the standard addition method or by forming a calibration curve using only one standard solution.