Firma:              Rheodyne Ventil

Modell:            7725 i

Kommentar:   Dokumente engl.

Models 7725/7725i and 9725/9725i

Sample Injectors for HPLC

Figure 1. Rheodyne 7725/7725i stainless steel (left) and 9725/97251 PEEK (right) front Iosding sample injection valves for HPLC

Rheodyne 7725/7725i and 9725/ 9725i front loading HPLC Sample Injectors are easy to use, and provide chromatographers with the Rheodyne Hallmark of Excel­lence... unparalleled performance and exceptional product lifetime.

•            Patented Make-Before-Break (MBB ^TM ) architecture virtually eliminates transient pressure shocks for extended column life

•            Available in stainless steel and PEEK for sample compatibility

•            Zero sample Ioss

•            2 µL internal sample loop accessory available

•            Wide 30° port angles for easy access

•            Position sensing switch built into "i" models

•            Small diameter internal flow paths assure minimal dispersion

MBB Flow Design for Pressure Shock Reduction

Rheodyne's exclusive MBB flow architecture virtually eliminates pressure transients. The high pressure flow from the pump is uninterrupted when the injector is switched between LOAD and INJECT, a benefit when using flow sensitive detectors, fragile columns, or pumps that are disturbed by flow or pressure transients.

Fig.2 shows column pressure vs. time for MBB (upper curve) in comparison to non-MBB sample injectors (lower curve).

Fig. 2 shows column pressure vs. time for MBB (upper curve) in comparison to non-MBB sample injectors (lower curve).

A passage in the stator face assembly makes new connections before old ones break. This patented Make-Before-Break (MBB) design is an improvement over in­jectors which use a bypass. lt is easy to troubleshoot, and does not dilute sample.

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Mechanical Design

The Interface between the rotor and sta­tor face is the location of the flow switch­ing and high-pressure sealing. This In­terface is a flat surface, and consists of a rotor seal made of an inert polymer, and a ceramic stator face assembly. The highly-polished ceramic does not scratch or wear under normal use.

As a result, a rotor seal should last for tens of thousands of injections in normal use, and shed very few particles

Figure 3. Pressure loss of stainless steel/poly­mer valve (top) and Rheodyne ceramic/polymer valve (bottom) vs. thousands of injections.

Position Sensing "i" Injectors

In the 7725i and 9725i valves, turning the valve to INJECT closes a built-in position sensing switch, which remains closed until the valve is returned to LOAD. When the position sensing switch wires are attached to a chromatograph, the switch provides the System with a reproducible start signal.

Zero Sample Waste

A syringe needle with a flat end (square cut) must be used. When the needle is inserted into the needle port, the tip of the needle passes through a seal inside the rotor seal, and then contacts the ce­ramic stator face. This direct connection between the tip of the needle and the end of the loop eliminates sample holdup. All sample leaving the needle enters the loop, so there is zero sample waste.

Leak Tight Needle Seal

The needle seal is a Teflon sleeve that is built into the rotor seal. lt grasps the tip of the needle, aligning it with the loop passage, and assures that all sample dispensed from the syringe enters the loop. The seal is under compression from an internal spring, which maintains a leak-tight, self-adjusting seal around the needle.

Sample Injection

The needle port of each injector is built into the valve's handle. When the injec­tor is mounted an a panel, the handle and needle port are in front (Fig. 4A). In back of the panel are the body and the stator. The stator contains six tubing ports (Fig. 4B) for connecting the pump, column, sample loop, and vent lines.

Fig. 4A shows a cut-away view of the valve in both the LOAD and INJECT po­sitions. Below the cut-away view is an illustration of the internal flow passages. The six circles represent the ports in the stator. The arcs represent the connecting passages in the rotor. The needle port is shown aligned with port 4.

In the LOAD position mobile phase flows to the column via port 2, a rotor passage, and port 3. The loop, which contains mo­bile phase trapped when the injector was returned to LOAD, can be partially or

completely filled with sample from a syringe via the needle port, which aligns with port 4. The mobile phase displaced by the sample exits the loop via drain at port 6.

With the syringe still in the needle port the valve is turned to clockwise through 60 ° to INJECT. Channels in the rotor seal now directthe mobile phase intotheend opposite from where the sample entered the loop. Note that the sample travels in a direction opposite to the direction during loading; it does not have to pass through the entire loop. The needle port and sy­ringe now align with drain at port 5. When the needle port is flushed, the flushing solvent exits directly out this port without entering the sample loop. The needle port and syringe are never exposed to high pressure. The loop is self-cleaning, be­ing continuously flushed by mobile phase during analysis.

VERSATILE INJECTION METHODS

Rheodyne front loading injection valves operate as follows: Sample is first LOADED into the sample loop by dis­pensing it from a syringe (Fig. 5) or by pulling it through a dip tube using a Suction Needle Adapter (Fig. 6). Sample is then INJECTED onto the column by turning the handle, which connects the loop to the high-pressure mobile phase stream. These versatile injectors offer a choice of three loading methods: Com­plete, Partial, and Suction.

Sample Injection using

Complete Filling Method

When injection volumes do not often change, or when sample conservation is not required, complete filling is the method of choice. The complete fill method produces excellent volumetric precision, typically about 0.1% relative standard deviation. Sample is dispensed from a syringe, using an excess amount

(at least 3 times the loop volume) to dis­place all the mobile phase in the loop. The loop sets the volume injected; the volume is varied by changing the loop size. Since the loop sets the volume, this method does not require precise use of the syringe.

Sample Injection using

Partial Filling Method

Applications where injection volumes change frequently, or when sample con­servation is important, partial filling is the method of choice. Volumetric accuracy and precision depend an the operator's ability to read and use the syringe, typi­cally about 1%. The volume injected is determined by the amount dispensed into the loop by the syringe. The amount dispensed must be less than half of the total loop volume. The partial fill method does not waste sample, and allows the volume to be continuously varied without changing the loop.

In partial filling (load no more than 50% of the loop volume), all of the sample dispensed from the syringe needle enters the loop, even with samples as small as 0.1 uL. There is zero sample waste.

Sample Injection using

Suction Method

Rheodyne 9725 (PEEK) valves have no metal in contact with the flow stream. The preceeding methods expose sample to the metal needle of the syringe. Though the exposure is small, metal can be completely avoided by using a syringe to suck sample into the loop via a PEEK tube at port 6. Using this method the tube end is placed into the sample vial. An empty syringe is inserted into the needle port, and used to pull sample into the loop. Model 9125-076 Suction Needle Adapter, an accessory listed under order­ing information, is recommended forthe suction method. As shown in Fig. 6, the adapter makes suction loading easier.

SPECIFICATIONS

Stainless Steel Model:       7725 and 7725i

Maximum Pressure:          48 MPa (482 bar, 7000 psi)

Wetted Surfaces:              316 stainless steel, alumina ceramic, and an inert polymer

pH Range:                         0-10 (pH >10, contact factory)

Maximum Temperature:     80°C

Flow Passage

Diameters:                         0.6 mm (0.024") and 0.5 mm (0.018")