The Multi-Commuted Flow Analyser

Addition, removal or exchange of manifold components, re-directing of flowing streams and establishment of tandem streams are easily and efficiently accomplished by multi-commutation. 

Multi-commuted flow systems [107] have similar characteristics to the flow systems described above. They comprise several discrete commuting devices, e.g., valves and pumps, strategically positioned in the manifold to provide enhanced versatility, and hence high performance [108], and even a novel type of flow system [109]. 

Sample dispersion in multi-commuted flow systems is governed by the same parameters as in other flow systems. However, the manifold status can be modified by the operation of these discretely operated devices. Consequently, external timing of the various committed devices is an important aspect of controlled sample dispersion, as emphasised below. 

Sliding bars and rotary valves were the first devices to be exploited for commutation. They operate in two positions (Fig. 6.10) and were initially used to insert a selected volume of sample into a carrier stream by means of a sampling loop. In the load position, the loop is in the sample-loading channel and the inlet and outlet ports of the carrier stream channel are 

With two rotary valves or a sliding bar valve with two commutation sections [110], two solutions can be sampled and inserted, and this is the essence of flow systems exploiting, e.g., merging zones or zone sampling (see 7.1.1 and 7.2.1). 

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