Injection and Multi-functional Valves

The author will not refer exhaustively to the various valve designs reported in the literature, since some of the earlier designs, such as the membrane type and sandwich type rotar valves, described in. some other monographs [3.4]. are now. seldom used. Only those designs which are used most frequently in on-line. separation. systems will be described in this section. 

The principle of operation of a two-layer six-port rotar valve, with its design borrowed from HPLC valves, is shown in Fig. 2.3. The valve has three channels engraved on the contact surface of the rotor and six pons on the stator, or vice versa. The valve is simple in construction, but is not sufficiently versatile to perform the more complicated functions often encountered in on-line. separations, in which case a group of such valves may be used to achieve the desired performance. 

FigJJ Schetnaiic diagram of a 6-port injector valve. S. sample NS. new sample C. carrier D. reaction coil and detector L, sample loop and W. waste. 

4 8-channel 16-pon multifunctional valve as used in dual column ion-exchange preconcentration for flame AAS. S, S2, samples 1, 2, eluent, Ci, C2. ion-exchange columns AAS. AA spectrometer, and W, waste (cf. Fig. 2.5 d) ref. [5] by permission of lsvier scientific Publishing Co.. 

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Only general purpose equipment used in FI systems is described in this chapter, together with its proper usage, particularly in separation and preconcentration applications. Included are solution delivery (propulsion) devices, injection and multi-functional valves, transport and mixing systems, and the most frequently used detectors. Devices used for specific separation purposes are described in the corresponding chapters on individual separation techniques. 

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