Valves eight-port

LC/LC (eight-port valve) Emi and Frei (1978) Bushey and Jorgenson (1990)... 

FIGURE 5.5 2DLC with eight-port valve and two sample loops. In position A, loop 1 (LI) is being loaded with sample from column 1, and loop 2 (L2) is being injected onto column 2. In position B, L2 is being loaded with sample from column 1, and LI is being injected onto column 2. 

Another technique, which is much more frequently employed, relies on commercially available multiport valves with a large number of sampling loops (an example is a valve carrying 16 sampling loops, with 16 positions and 2 x 16 + 2 = 34 ports, i.e., two for each loop plus a gas entrance and a gas exit port). The simplest arrangement of such a multiport valve downstream of the catalytic reactor is shown in Fig. 7 (for the sake of simplicity, only two sampling loops are drawn). The multiport valve is assisted by an eight-port valve with two positions. The needle valve is to com-... 

To inject two samples of different quantities from one duct of the gas under analysis, a two-position, eight-port valve with two sample loops is used (Fig. 6). In position A, the carrier gas flows through sample loop 1 into a... 

A further operational area is working with two guard columns for enrichment purposes and one main column. As long as one guard column takes to load, the other one is in the separation cycle. For this, an eight-port valve is necessary. This variant allows an increase in sample throughput for rapid analyses. 

In 1993, Jorgenson s group improved upon then earlier reverse phase HPLC-CZE system. Instead of the six-port valve, they used an eight-port electrically actuated valve that utilized two 10-p.L loops. While the effluent from the HPLC column filled one loop, the contents of the other loop were injected onto the CZE capillary. The entii e effluent from the HPLC column was collected and sampled by CZE, making this too a comprehensive technique, this time with enhanced resolving power. Having the two-loop valve made it possible to overlap the CZE runs. The total CZE run time was 15 s, with peaks occurring between 7.5 and 14.8 s. In order to save separation space, an injection was made into the CZE capillary every 7.5s,... 

An eight-port or a ten-port valve with dual matching sample loops is generally used for automated comprehensive 2DLC so that solute is injected repetitively into the... 

Figure 12 Schematic representation of 2D chromatography using an eight-port injection valve and two storage loops. (A) In the first position of the valve the storage loop 1 is loaded with the HPLC eluent, while the content of the storage loop 2 is analyzed by SEC. (B) In the second valve position storage loop 2 is loaded with HPLC eluent and the content of loop 1 is analyzed according the molecular size of the solute.

Figure 23. Realization of the enantioselective SMB liquid phase approach by using eight 15 cm x 20 mm (i.d.) columns containing Chiralcel OD. 1 columns. 2 LC-pump. 3 eight-port rotary valve. 4 back-pressure-valve, 5 feed reservoir (racemate). 6 desorbent reservoir. 7 extract (enantiomer 1) and raffinate (enantiomer 2) collector. 8 system controller (Negawa and Shoji, 1992).

Like gated EK injection, gated FID injection was achieved (see Figure 4.23). Sample injection volumes from 0.5 to 10 nL were made in real-time [569]. FID injection conducted in the pinched and gated modes was achieved on a PET chip using three syringe pumps and an eight-port rotary valve [570]. 

The most sophisticated way of coupling the two chromatographs is a fraction transfer system comprising one eight-port injection valve (see Fig. 15). With two storage loops, it is possible to collect fractions continuously without losses. When starting the separation, loop 1 is in the LOAD position, whereas loop 2 is in the INJECT position. Each of the loops has a volume of 100-200 pi. When the first fraction leaves the HPLC system, it enters loop 1 and fills it. When loop 1 is completely filled with the fraction, the injection valves automatically switch to the opposite positions, i.e. loop 1 is then connected to the SEC system in the... 

Fig. 15. Schematic representation of 2D chromatography using an eight-port injection valve and two storage loops...

FIGURE 22 Scheme of the eight-port switching valve for successive online transfer of sample fractions between the Id and 2d columns. The effluent from the Id column (C l) is transferred into the 2d column by means of the switching valve with two loops. P 2 is the second pump. 

A single eight-port injection valve can perform the same functions as two six-port valves as it can accommodate two loops. This type of valve is commonly used in gradient and sandwich techniques, where the sample is sandwiched between the carrier and a solution containing a reagent or a standard, and then returned to the carrier. 

For most applications, the LC column (or the first of two columns) is backflushed with a stronger solvent after every sample in order to remove the matrix material. This presupposes a backflush valve of eight ports and a pressurized flask supplying flushing solvent to the backflush loop. 

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