Abstract: The effects of continuous, pulsed and stopped flow on the dispersion of a sample injected into a µflow injection system were studied. A channel with a volume of 1 µl was used to compare experimental results with numerical results. The injection was 0.067 µl of bromocresolgreen solution into a borax solution, the detection volume was ~0.047 µl. To study the effect of the flow rate, response curves were measured at 0.5, 1.0, 2.0, 3.0, 4.0 and 5.0 µl min-1. Different time intervals ranging from 10 to 400 s were used to investigate the effect of stopped flow. The effect of pulsed flow was studied at different frequencies ranging from 5 to 0.1 Hz. The results for continuous flow obtained with the numerical model are in agreement with the experimental values. For stopped and pulsed flow there is a small difference between the experimental and numerical results that can be explained by the value of the adopted numerical diffusion coefficient. A decrease in the (continuous) flow rate causes a decrease in the dispersion of the sample. The results obtained with a pulsed flow show no significant difference in comparison to the results obtained with continuous flow when the pulse frequency is above a lower limit. The lower pulse limit in the flow system used in this paper is 1 Hz. Stopped flow has virtually no effect on sample dispersion.

Abstract: Pulsed flow chemical (PFC) is described as a new approach to automated online anal. chemical In contrast to existing flow-based anal. chemical methods, PFC is characterized by pulsed flow, turbulent mixing and low axial dispersion. The PFC system is fully computerized and all operations are under software control. Consequently, most flow analysis methods (e.g., flow injection, continuous-flow, flow titration, etc.) can be selected with a simple click of the mouse. The system is easily miniaturized and portable which makes it particularly suited to field instrumentation. The system has been tested using several flow-based techniques including online titration for the determination of calcium in waters with potentiometric detection and a calcium ion sensor.