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Sequential Injection Analysis: A useful Analytical Tool in Drug Dissolution Testing

Paraskevas D. Tzanavaras

Sequential-injection analysis (SI) is considered to be the second generation of flow injection techniques and was initially developed by Ruzicka and Marshall [1,2] as an alternative sample-handling technique to the well-established Flow injection analysis (FI) [3-5]. As can be seen in a typical SI setup in Figure 1, the heart of a SI manifold is a multiposition selection valve. Fluids are manipulated within the manifold by means of a bi-directional pump. A holding coil is placed between the pump and the common port of the multiposition selection valve. The selection ports of the valve are reservoirs, detectors, pumps, reactors, separators, special cells, other manifolds etc. After aspiration of a discrete volume (zone) of sample into the holding coil via the sample line, the sample can be subjected to very complex physical and chemical pre-treatment in different ways within the SI manifold. SI offers great potential for sample handling because it is a bidirectional, stopped-flow sample-handling technique enabling the sample to be serially processed in the different modules connected to the selection valve by means of repetitive aspiration and delivery steps. The advantages of SI over FI are the following: a) SI makes use of a simpler manifold that can be employed for a larger range of analytical methods without (or minimal) alterations in its physical configuration; b) in SI, discrete volumes of sample and reagents are aspirated and their consumption is drastically reduced; c) the bidirectional and stopped-flow operation of SI provides great scope for pre-treatment of the sample. This last attribute of SI makes it ideally suited to clinical and biochemical applications for which sample pre-treatment is usually necessary prior to the actual analytical measurement.