AUTOMATIC CALIBRATION IN CONTINUOUS-FLOW ANALYSIS

A manifold which permits calibration graphs to be obtained automatical ly during continuous flow analysis is discussed. The entirely computer -controlled system is based on the use of two variable-speed peristalt ic pumps. One of the pumps moves a standard solution of the analyte an d the other displaces a diluent solution, both solutions being merged before reaching the detector. The flow rate delivered by the first pum p is increased linearly with time, while that of the second pump is de creased linearly at the same rate. In this way, an on-line concentrati on gradient is obtained, the flow rate through the detector remaining constant. The signal-time profiles thus obtained can be used for calib ration graphs after suitable treatment of the data. A sample solution can then be quantified by pumping it continuously through the manifold . The system is versatile and easy to handle since it is easily adapte d to determinations which need a previous chemical reaction, and the s ame computer that controls the pumps also acquires and treats the sign al-time data. The performance of the system is first discussed and the n experimentally checked by using two common spectrophotometric determ inations. The experiments prove that the approach, which can be extend ed to other detection systems, is highly reproducible and accurate. In addition, the manifold permits the on-line dilution (up to ten times) of samples which are too concentrated to be measured directly. A savi ng of time and reagents can be achieved since, if needed, reliable cal ibration can be obtained in 50 s while only 145 mu l of a single stand ard solution is consumed.