131
Valves
HighPressureDualMode Sample Injectors
Models 7725(i), 9725(i), 8125, and 3725(i)-038
316 stainless steel
Available in analytical, micro, and
preparative scale
Make-Before-Break (MBB
®
) architecture
allows continuous fow between LOAD
and INJECT positions which greatly
reduces transient pressure shocks that
disrupt your system
Wide, 30° port angles offer easier
access to fttings using the
IDEX Wrench (Part No. 6810 on
page 140)
Front-end pressure screw
makes it easy to adjust and
maintain pressure
A built-in position sensing
switch (“i” versions) provides the
chromatograph with a reproducible start signal
TheMBB valve design is illustratedbelow. In the LOADposition, mobile
phase fow from pump port to column port travels through both the
rotor seal groove and the MBB passage (Position A). As the rotor seal
grooves rotate to change from LOAD to INJECT, there is continuous
mobile phase fow through both one rotor seal groove and the MBB
passage (Position B) until the rotation stops and both rotor seal grooves
are connected by the loop. Sample fow begins through the loop to
the column just as all fow stops through the MBB passage (Position
C). Sample fow never enters the MBB passage. Valve fow passages
are 0.6 mm (0.024”) in diameter.
Manual Injector Valves
Part No. Description
Pressure Rating Sample Loop Included Tubing/Fittings Size
Wetted Material
High Pressure Manual Injectors
3725
Preparative Scale Dual Mode Injector
4,000 psi (276 bar) 10 mL
5/16-24 ports for 1/8” Tubing
PEEK
™
3725-038 Preparative Scale Dual Mode Injector
5,000 psi (345 bar) 10 mL
5/16-24 ports for 1/8” Tubing
Stainless Steel
3725i
Preparative Scale Dual Mode Injector with Switch
4,000 psi (276 bar) 10 mL
5/16-24 ports for 1/8” Tubing
PEEK
3725i-038 Preparative Scale Dual Mode Injector with Switch
5,000 psi (345 bar) 10 mL
5/16-24 ports for 1/8” Tubing
Stainless Steel
7725
Analytical Scale Dual Mode Sample Injector
5,000 psi (345 bar) 20 µL
10-32 ports for 1/16” OD Tubing
Stainless Steel
7725i Analytical Scale Dual Mode Sample Injector, with Switch 5,000 psi (345 bar) 20 µL
10-32 ports for 1/16” OD Tubing
Stainless Steel
8125* Micro Scale Dual Mode Sample Injector with Switch
5,000 psi (345 bar) 5 µL
10-32 ports for 0.020” (0.5 mm) or 1/16” Tubing Stainless Steel
9725
Analytical Scale Dual Mode Sample Injector
5,000 psi (345 bar) 20 µL
10-32 ports for 1/16” OD Tubing
PEEK
9725i Analytical Scale Dual Mode Sample Injector with Switch 5,000 psi (345 bar) 20 µL
10-32 ports for 1/16” OD Tubing
PEEK
*The 8125 requires special ferrules for 0.020” (0.5 mm) tubing. 8125-084 – 0.5 mm ferrule for 8125; 8125-086 – 0.5 mm ferrule for 8125 - 4-pk.
Dual Mode Sample Loop Loading:
Partial-Filling vs. Complete-Filling
Partial-Filling
Use the partial-flling method if you need to conserve sample, or if you want
to vary sample volume frequently.
In partial-flling, the syringe sets the volume injected onto the column.
There is no sample waste, and the volume injected onto the column is equal
to that dispensed from the syringe. Reproducibility is 1.0% relative standard
deviation (RSD). The volume of the sample loaded is limited to half the
sample loop volume. For example, the most you can load into a 200 µL
sample loop is 100 µL.
Complete-Filling
Use the complete-flling method if you have plenty of sample, if you do not
vary sample volume, or if you need high reproducibility.
In complete-flling, the loop sets the volume loaded onto the column. Use
excess sample (two to fve loop volumes) to replace all the mobile phase
in the loop. See Figure 2. Change the loop to vary the sample volume.
Reproducibility is typically 0.1% RSD for loop sizes ≥ 5 µL. Accuracy is limited
as loop volumes are nominal.
Q:
“Which method should I use and which Rheodyne
®
sample injectors use
this method?”
A:
There are two types of injectors available: dual mode and single mode.
Dual mode injectors allow both partial- and complete-flling whereas
single mode injectors allow only complete-flling. See Sample Injectors
on pages 129 – 132.
If you are collecting experimental data, sample is scarce, and/or you want
to use different sample volumes, a dual mode injector with a large volume
sample loop is appropriate. Only dual mode injectors allow the partial-
flling method for easily varying your volumes (up to half your sample loop
volume) by setting the syringe volume. Once you begin routine analysis,
and/or you have an abundance of sample, either a dual mode or single
mode injector is appropriate. Both types of injectors allow the complete-flling
method in which you overfll the sample loop. Complete-flling maximizes the
reproducibility of your results.
Application Note
Flow path for the typical dual mode injector
INJECT
LOAD
Waste
Waste
1
3
4
5
6
2
Column
Needle Port
Pump
Waste
1
3
4
5
6
2
Needle Port
Waste
Pump
Column
Flow paths of model 7725(i) and 9725(i) with MBB design
Make-Before-Break Design
Rotor Seal Grooves
Rotor Seal Grooves
MBB Passage
MBB Passage
Position B
Position C
Position A
Shaft End
Rotor Seal
Stator
Face
Stator
Rotor Seal
Groove
Stator Face
Seal
Column
Pump
MBB Passage
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