Continuous, pulsed and stopped flow in a μ-flow injection system (numerical vs experimental) Original Research Article

The effects of continuous, pulsed and stopped flow on the dispersion of a sample injected into a μ-flow 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 ca. 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.