I.5.
Sequential Injection (SI), (Chapter 2), was initially designed for continuous monitoring of industrial processes, where robustness, low reagent consumption, automated calibration and long time stability are the essential requirements (Ruzicka & Marshall 1990). In contrast to continuous flow techniques SI is based on discontinuous flow, which is programmed to move sample and reagents forward as well as in reverse. This flow programming reshapes the parabolic flow profile, promotes mixing of the sequentially injected zones and allows reaction rate measurements to be carried out in stop flow mode.
Flow Programming for Sequential Injection
The mini SI flow scheme, shown here in lab-on-valve configuration, comprises a pump, a holding coil a multiposition valve and a flow trough detector. Microliter volumes of sample and reagents are sequentially stacked within the holding coil and by following flow reversal transported into the detector. Flow programming reduces reagent consumption and waste generation, since the flow is discontinued during sample incubation period and between individual measurements. The movie clip shows programming of microfluidic manipulations.
Bead Injection (BI), (Chapter 3) is a variant of SI technique, adapted to handle suspensions with aim to meter, transport, capture, perfuse, monitor and discharge microspheres, such as chromatographic materials in order to miniaturize and facilitate separations‘ trough automated renewal of the stationary. BI spectroscopy is based on monitoring of captured beads, while renewable column separations rely on monitoring of eluted species.
J. Ruzicka & G.D. Marshall, Anal. Chim. Acta, 237, 329, (1990).