Six-port valve

Figure 6.12 Schematic diagram of the interface used for direct SFE-CEST coupling without a sample pre-concenti ation step 1, micro-LC pump 2, heated restrictor 3, six-port valve 4, direct by-pass to the CE unit 5, three-port valve 6, CE instmment. (from ref. 58).

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,... 

A six-port valve was first used to interface the SEC microcolumn to the CZE capillary in a valve-loop design. UV-VIS detection was employed in this experiment. The overall run time was 2 h, with the CZE runs requiring 9 min. As in the reverse phase HPLC-CZE technique, runs were overlapped in the second dimension to reduce the apparent run time. The main disadvantage of this yu-SEC-CZE method was the valve that was used for interfacing. The six-port valve contributed a substantial extracolumn volume, and required a fixed volume of 900 nL of effluent from the chromatographic column for each CZE run. The large fixed volume imposed restrictions on the operating conditions of both of the separation methods. Specifically, to fill the 900 nL volume, the SEC flow rate had to be far above the optimum level and therefore the SEC efficiency was decreased (22). 

Figure 14.8 Schematic diagram of the natural gas analyser system SL, sample loop VI, two-way valve to block the sample lines V2, ten-port valve V3, V4 and V5, six-port valves R, restriction TCD, themial-conductivity detector FID, flame-ionization detector.

The use of IR pulse technique was reported for the first time around the year 2000 in order to study a catalytic reaction by transient mode [126-131], A little amount of reactant can be quickly added on the continuous flow using an injection loop and then introduce a transient perturbation to the system. Figure 4.10 illustrates the experimental system used for transient pulse reaction. It generally consists in (1) the gas flow system with mass flow controllers, (2) the six-ports valve with the injection loop, (3) the in situ IR reactor cell with self-supporting catalyst wafer, (4) the analysis section with a FTIR spectrometer for recording spectra of adsorbed species and (5) a quadruple MS for the gas analysis of reactants and products. 

FIGURE 5.2 Heart-cut 2DLC with a six-port valve. In position A, the loop is being loaded with a sample from column 1, and column 2 is being equilibrated. In position B, the loop is injected onto column 2 where separation takes place with subsequent detection. 

Fig. 5.3 displays a schematic for the HPLC configuration using two six-port valves along with the steps employed for the quantitative analysis of antibodies in serum... 

The loss of about 7% of the lst-D effluent caused by a 2-s injection in a 30-s operation cycle, which could cause up to 20% loss of a peak in the most unfavorable case, or the narrowest peak at the beginning, can be avoided by using two six-port valves each having a sample loop (Fig. 7.6b) an alternative system uses a 10-port valve with two holding loops. The loops hold the effluent of the lst-D alternately for 30 s during a complete separation cycle on the 2nd-D column to effect comprehensive 2D HPLC. 

Figure 6 Schematic diagrams of atypical high-pressure SF-CL systems based on special mixing modes (a) system based on conventional propelling and stopping syringe and (b) system based on liquid chromatographic (LC) pumps and stopping the flow before the mixer (M). V, six-ports valve. (Adapted from Refs. 33 and 34.)...

A six-port valve was used in both manual and semi-automated SPME interfaces and PEEK tubing used to connect the HPLC system to the SPME probe. A Cohesive HTLC 2300 with dual pumps along with a Sciex API 3000 mass spectrometer was used for LC/MS/MS and a Symmetry Shield RP-18 (5 ji, 50 x 2.1 mm) for HPLC. A quaternary pump with flow switching was used for desorption chamber flushing along with MS make-up flow and a binary pump for LC/MS/MS. Acetoni-trile/0.1% acetic acid in water (90 10, solvent B) and 10 90 acetonitrile/0.1% aqueous acetic acid (solvent A) were used, with 10% B for 0.5 min ramped to 90% B in 2 min and held at this concentration for 1.5 min before returning to 10% B for 1 min at a flow rate of 0.5 mL/min. 

Typical instrument set-ups for online sample preparation, for example, solid phase extraction and sample pre-concentration, require the control of a six-port valve with an additional special column and a second pump. Ideally, this system will be fully controlled by the data acquisition software (Figure 3.12 (A)). 

Details of the trap heater are also shown in Figure 2. The adsorption-desorption cycle may be accomplished conveniently with the use of a six port valve and a plumbing system constructed of materials that neither adsorb volatile organics nor outgas... 

Most of the autosamplers have a piston metering S3rrmge t)rpe pump to suck the preestablished sample volume into a line and then transfer it to the relatively large loop ( 100 ml) in a standard six-port valve. The simplest autosamplers utilize the special vials with pressuarization caps. A special plunger with a needle, push the cap down to the vial and displace the sample through the needle into the valve loop. Most of the autosamplers are microprocessor controlled and can serve as a master controller for the whole instrument... 

Graham and Garrison (17) evaluated on-line trace enrichment for the determination of trace organic compounds in aqueous environmental samples. These workers were primarily interested in nonvolatile and thermally labile compounds that were not readily analyzed by GC methodology. A 2-mm i.d. X 70-mm long stainless steel precolumn was packed with 30-75 pm diameter octadecyl-derivatized silica. This precolumn was substituted for the sample loop in a conventional, high-pressure, six-port valve. Water samples, 10-100 mL, were pumped directly on the precolumn. After loading, the valve was switched to... 

Injection devices are all six-port valves. Sample loops have different volumes. Volumes of the sample loop must be adapted to the column diameter (61). Increases in the volume of very dilute solutions do not destroy efficiency, but increases in both the volume and amount of solute are detrimental. 

---