HIGH PRESSURE SWITCHING VALVES

Transcription

1 HIGH PRESSURE SWITCHING VALVES Rheodyne offers high pressure switching valves to simplify procedures and improve the speed, resolution, and sensitivity of HPLC analysis. The switching valves are available in stainless steel, titanium, and PEEK. The stainless steel and PEEK valves are available with 1/16- and 1/8-inch ports. There are two major areas of application: column switching and column selection. Column Selection These valves substitute one column for another without the need to manually disconnect the plumbing. This makes it easy to dedicate a separate column to each analysis. Dedicated columns eliminate equilibration delays, reduce interferences, and prolong column life. The valve is simply turned to select the column desired for a particular analysis. The columns switched off-line are automatically sealed at both ends. The various models each have unique column selection capabilities, discussed on pages Column Switching These valves re-route mobile phase during the chromatographic run, with no change in the mode of separation (such as backflushing and fraction cutting), or with changes, using sequential separation with different columns and/or mobile phases (such as trace enrichment, sample clean-up, and coupled-column analysis of complex samples). The Model 7000 (and its titanium and PEEK versions) is the most generally useful valve for column switching. But other models are better in certain cases. Examples are illustrated on page 20. Table V. Specifications of Switching Valves Model 7000,7030,7040 (SS & Titanium) Passage Diameter.6 mm 7060 (SS).4 mm 7000L,7030L,7040L, 7060L(SS & Titanium) 1.0 mm 9010,9030,9060 (PK).4 mm 3000,3030,3060 (PK) 1.0 mm , , (SS) 1.0 mm Factory Set Pressure 3000 psi (207 bar) 3000psi (207 bar) 4000 psi (276 bar) SS = stainless steel PK = PEEK *Titanium valves have a maximum temperature of 50 C, due to the Tefzel rotor seal. Many Rheodyne switching valves can be easily converted from one model to another. Model 7040 is a 7000 with an external loop across ports 1 and 5. The Model 7030 is a 7000 with a different rotor seal. Most models can be field-retrofitted with a pneumatic actuator. Valves with factoryinstalled actuators are designated by the letter "P", e.g. Model 7000P. Many models are available in a standardbore and a large-bore "L-version". The large-bore and/or the 1/8-inch valves can be used when the pressure drop must be limited. See the graph on page 10. Max. Field Set Pressure 7000 psi (483 bar) 7000 psi (483 bar) 4000 psi (276 bar) Maximum Temp. *

2 Six-position Column Selection Valves Tandem Rheodyne offers manually operated selector valves of different sizes and materials. The models that accept 1/16-inch fittings are: 7060 (stainless steel), (titanium), and 9060 (PEEK). Those that accept 1/8-inch fittings are: 3060 (PEEK) and (stainless steel). You can select among six columns for different analytical methods on the same chromatograph. This has several advantages over manually changing columns: selection is immediate, fittings are not subjected to the wear of repeated tightening, and the valve seals the off-line columns at both ends and keeps them on standby for future use. The common (center) port of this valve connects to the injector. Turning the valve handle directs flow into one of up to six columns connected to the six peripheral ports. A second valve is placed at the column outlets to select the operating column effluent and direct it to the detector. It is useful to use the sixth port for a bypass/ flush-out tube. This permits rapid mobile phase chageover, without exposing any column to a mobile phase other than the one with which it is routinely used. This scheme is shown above. Note that two separtate valves are required. The valves accepting 1/16-inch fittings have internal passages of 0.4-mm I.D., with a total internal volume less than 2 µl. This has an insignificant effect on resolution, as discussed on page 19. The valves accepting 1/8-inch fittings and the large-bore "L-versions" are used in applications where excessive pressure drop must be avoided. See page 15 for specifications and page 18 for pressure drop information. These valves can be used for mobile phase selection by connecting the common (central) port to a pump inlet. See page 23 for economical alternatives using Type 50 Teflon valves. The valves have a spring-loaded detent mechanism which allows continuous rotation in either direction and ensures that the shaft "falls into" each position at the precise 60 spacing position Valve 7060P 6-position valve with 7060L 7060LP 6-position Large Bore Valve 6-position Large Bore Valve with Titanium Valve 9060 PEEK Valve 9060P PEEK Valve with 3060 PEEK (1/8-inch) Valve 3060P PEEK Valve with Stainless Steel (1/8-inch) Valve P Stainless Steel Valve with The Tandem consist of two six-position valves mounted on a common pneumatic actuator. The valve rotors are geared together so that they turn simultaneously. This product allows the connection of up to six columns, or five columns and a bypass/flush-out tube which allows solvent changeover to be made without flow through any column. The actuator is controlled by the Model 7164 Air Control Valve (supplied), but can also be controlled by a programmer via a solenoid air valve (not supplied, see page 22). The column in use is indicated by a pointer on the actuator shaft. A six-position electrical switch is mounted on the shaft, permitting remote indication of valve position. The tandem actuator requires compressed gas: minimum 80 psi (6 bar), maximum 100 psi (7 bar) Tandem 7066L Large Bore Tandem Titanium Tandem 9066 PEEK Tandem 3066 PEEK (1/8-inch) Tandem Stainless Steel (1/8-inch) Tandem

3 Column Switching Valves Two-position six-port switching valves are available in different sizes and materials. The models that accept 1/16-inch fittings are: 7000 (stainless steel), (titanium), and 9010 (PEEK). The models that accept 1/8-inch fittings are 3000 (PEEK) and (stainless steel). Turning the handle back and forth 60 switches the flow paths from the solid lines to the dashed lines illustrated above. These valves have many column switching uses, where the flow is redirected among columns during the chromatographic run. Applications include trace enrichment, Sample clean-up, and coupled-column analysis (see the diagrams on page 20). These valves are also useful for selecting between two columns, as illustrated above and in Fig. 8. Compare them with the three-way valves on page 18, in which each end of the off-line column is independently sealed, instead of connected together head-to-tail. If switching is done before all pressure has bled from the column, independent seals produce less shock to the column. Model 9010 PEEK injector (see page 7) is listed here because it can be converted to a switching valve functionally identical to Model 7000 by removing the loop Switching Valve 7000P Switching Valve with 7000L 7000LP Large Bore Valve Large Bore Valve with Titanium Valve L Large Bore Titanium Valve 9010 PEEK Injector 3000 PEEK Valve (1/8-inch) Stainless Steel Valve (1/8-inch) from pump Sample Injector to detector Column Selection Valve Figure 7. In this photograph the Model 7000 Switching Valve is connected to select between two columns, one 10 cm and the other 15 cm. Turning the valve handle selects one of the columns for the injector-to-detector flow path and places the other column off-line, sealing it and keeping it in standby condition. A Model 7125 Sample Injector is shown connected to the selection valve.

4 Three-way Valves Four-way Valves Two-position six-port valves with a double three-way switching pattern are available in different sizes and materials. The models that accept 1/16-inch fittings are: 7030 (stainless steel), (titanium), and 9030 (PEEK). The models that accept 1/8-inch are: 3030 (PEEK) and (stainless steel). Turning the handle back and forth 60 switches the flow paths from the solid lines to the dashed lines illustrated in the figure above. You can perform the column switching schemes shown in Figs. 11f and 11l way Valve 7030P 3-way Valve with 7030L 7030LP Large Bore 3-way Valve Large Bore 3-way Valve with way Titanium Valve way PEEK Valve 9030P 3-way PEEK Valve with way PEEK Valve (1/8-inch) way Stainless Steel Valve (1/8-inch) Model 7040 is a six-port two position valve with an external loop, which exchanges the flow pattern from ports (2 3 and 4 6) to (2 6 and 4 3). See Figs. 11c, 11j, and 11k. Model 9010 can be converted to a 4-way valve by changing the loop to ports 1 and 5. Model 3000 can be converted by adding an external loop to ports 1 and way Valve 7040P 4-way/Pneumatic 7040L Large Bore 4-way Valve 7040LP Large Bore 4-way/Pneumatic way Titanium Valve Pressure Drop (psi) Pressure Drop (Atm) Flow Rate (ml/min) Figure 8. Pressure drop vs. flow rate for Model 7000 and Model 7000L (large-bore) valves; water at 20 C. Experimental measurements: The flow channel is one stator inlet port, one rotor seal groove, one stator outlet port, and two connectiong tubes. Solid squares = (1-mm 7000L valve) + (two 1-mm x 5-cm tubes). Open squares = (0.6-mm 7000 valve) + (two 1-mm x 5-cm tubes). Cross mark = (0.6-mm 7000 valve) + (two 0.5-mm x 5-cm tubes). Solid lines are theoretical values for 10-cm long tubes of 1 mm and 0.5 mm I.D.

5 Effect of Valves and Tubing on Resolution Rheodyne column selecting and column switching valves cause no observable loss of resolution with analytical columns when small-bore connecting tubing is used. Since dispersion caused by tubing is proportional to the fourth power of diameter, large-bore tubing should be avoided. A size 0.25 mm (0.010 inch) is recommended. The chromatograms in Fig. 10, made using a typical analytical chromatograph, show these effects. Fig. A is the control (injector column detector); no valves are in the system. In Figs. B, C, and D, two Model 7060 column selection valves were placed side by side (injector valve #1 column valve#2 detector), as illustrated above. The injector and detector were connected to these valves by the same tubing used in the control. The extra tubing pieces required to connect the valves to the column were a 10-cm length for valve#1 column and a 35-cm length for column valve#2. The diameters of these tubes are indicated in the figure. column only valve with.007 inch valve with.012 inch valve with.020 inch Figure 9. This shows the loss of resolutuon caused by the addition of two Model 7060 column selection valves when using connection tubes of three different inside diameters. Conditions for all cases: 4.6-mm x 12.5-cm column, 5 µm C-18 packing, 50% acetonitrile in water, 2 ml/min, 21 C, 5 µl sample partial-filled into a Model 7125 injector, 10-cm x 0.18-mm (.007-inch) bore injector outlet tube (to column or valve), 20-cm x 0.18-mm bore detector inlet tube (from column or valve), low-dispersion 1-cm path UV detector cell, 0.2-sec detector time constant. See text for details.

6 20a. Model 7000 Two-column selection A single two-positon valve can select either column A or column B. The off-line column is sealed by connecting head to tail. Switching should be done when the flow is off and the pressure is at zero. 20b. Model 7060 Five-column selection Two six-postion valves, one at each end of the columns, select between 5 columns and bypass/flush-out line. Offline columns are independently sealed. Two valves required. 20c. Model 7040 Column backflushing Flow direction can be reversed using a four-way valve. In this diagram, peaks are analyzed in the normal way, then the valve is switched and highly retained peaks are backflushed to the detector. Compare 20d. 20d. Model 7000 Pre-column backflushing Sample is injected into series-connected pre-column and analytical column. After valve switch, analytical column flow continues in normal direction. Only the precolumn is backflushed, eluting highly retained peaks directly to detector. 20e. Model 7000 Sample clean-up (stripping) Protects analytical column from proteins by irreversibly sorbing then onto precolumn. Analytes are also initially sorbed, but, after valve switch, a solvent change or gradient backflushes analytes into analytical column. Compare 20f, 20h. 20f. Model 7030 Sample clean-up (bypass) Protects analytical column from proteins by bypassing analytical column. Analytes are sorbed from buffer onto reversedphase pre-column. After valve switch a solvent change or gradient elutes analytes into analytical column. 20g. Model 7000 Sample clean-up (bypass) Identical to 20f, but using Model Here analytical column is isolated by connectiing head to tail. In 20f ends are independently isolated. This shows subtle differences between using different models. 20h. Model 7000 Sample clean-up (stripping) Unretained analytes pass through precolumn to analytical column where they are separated. Highly-retained undesired compounds are washed off the precolumn after valve switch. Two pumps required. Compare to 20e, 20f. 20i. Model 7000 Sample enrichment Large volumes of sample can be injected into the pre-column, where trace components are concentrated. After valve switch, sample is backflushed off pre-column into analytical column by the second pump. 20j. Model 7040 Alternating enrichment Similar to 20i, but two pre-columns save time. One is backflushed into analytical column while other reequilibrates and concentrates sample. The two precolumns alternate in their duty cycle. 20k. Model 7040 Alternating regeneration Two four-way valves can interchange two components between two flow streams. Here column A is regenerating while column B is analyzing. The columns then interchange by switching the two valves. 20l. Model 7030 Stop-flow scanning A three-way valve seals the column inlet, abruptly stopping the flow in the detector so that the peak can be scanned. The pumped mobile phase is diverted to drain line, so the pump need not be stopped.