Development of new automated flow titration systems

Titrimetry is one of the oldest analytical methods still in use. It is probably the analytical technique that has changed the least over the years. It remains one of the most widely used tools for making high precision measurement. In classical batch mode titration procedures, the volume of titrant added to a titration vessel is the variable that is controlled and monitored and subsequently used to calculate the original analytical concentration in the test solution. More advanced and automated batch mode titrators have been developed. However, the downside of titrations in conventional batch mode are significant reagent consumption and poor throughput rate. Thus, automation of titrations using the continuous flow mode has been increasingly drawing attention.

The new concept for continuous on-line titrations based on feedback-controlled flow-ratiometry and the principle of compensating errors creates a new paradigm for flow titrations by feedback based flow ratiometry in which the delay between the sample-titrant confluence point and the detector is made constant. The error due to lag time is continuously compensated for by averaging rapid backward and forward titrations. This new concept has been developed and applied to titrations followed by potentiometry and photometry.

Electrogeneration of titrants have several significant advantages. The most important of these is the elimination of problems associated with the preparation, standardization, and storage of titrant solutions. This advantage is particularly significant when dealing with unstable reagents. Electrogeneration of the titrant allows the transformation of the newly developed error-compensated feedback based flow-gradient method into a concentration gradient method. Coulometric titrant generation transfers the control from the flow control to current control. This system has been applied to various redox titrations using photometric and potentiometric detection methods.

An additional new type of flow injection titration system has been developed based on a syringe pump. In this system, the titrant is injected in a triangular programmed flow pattern by a syringe pump in a continuous stream of the sample. This new type of flow injection titration method was applied to acid-base and redox titrations, and the data interpreted by the principle of compensating errors.