SEQUENTIAL INJECTION ACID-BASE TITRATION - A USEFUL APPLICATION FOR PROCESS ANALYTICAL SCIENCE

A sequential injection (SI) titration system is proposed for the titra tion of a strong acid with a strong base. The concept is based on the sequential injection of a base titrant, acid analyte and a base titran t zone into a distilled water carrier stream, giving a stack of well-d efined zones adjacent to each other in a holding coil, which is swept by reversal through a reaction coil to the detector. The base zones co ntain Bromothymol Blue as indicator and the endpoint is monitored spec trophotometrically at 620 nm. A linear relationship between peak width and logarithm of acid concentration is obtained in the range 0.01 to 0.1 mol l(-1) of HCl with 1 x 10(-3) mol l(-1) of NaOH as titrant. Oth er linear ranges are possible by changing the titrant concentrations. The results obtained for the sequential injection titration of samples is in good agreement with a standard potentiometric method with an RS D < 0.30%. The system is fully computerised with a sample frequency of 30 samples h(-1).