3725I - 2/6 Prep. Inj., PK w/ Switch

The IDEX Rheodyne Model 3725I is a PEEK manual sample injector designed for reliable sample introduction in analytical liquid chromatography systems that require a metal-free flow path. Constructed primarily from PEEK (polyether ether ketone), the injector provides excellent chemical resistance while eliminating potential metal interactions with sensitive analytes.

The injector incorporates an integrated position sensing switch, allowing electronic confirmation of the valve position. This feature enables chromatography systems or external data acquisition hardware to detect whether the injector is in the LOAD or INJECT position, helping synchronize injection events with analytical data collection.

Like other Rheodyne manual injectors, the Model 3725I uses a Make-Before-Break (MBB) switching mechanism. This design ensures continuous mobile phase flow while the valve handle rotates between positions, preventing pressure disturbances and maintaining stable chromatographic baselines.

The injector features a front-mounted needle port for direct loop loading and is commonly supplied with a 20 µL sample loop. This configuration enables quick, reproducible manual injections for routine analytical LC workflows.

Engineered for biocompatible chromatography applications, the Model 3725I supports operating pressures up to 3000 psi (≈207 bar) and temperatures up to 80°C, making it suitable for a wide range of analytical LC methods while maintaining the advantages of a metal-free flow path.

Key Features

• PEEK valve construction for metal-free chromatography
• Six-port manual injector for analytical LC systems
• Integrated position sensing switch for injection confirmation
• Front needle port for direct loop loading
• Make-Before-Break switching for uninterrupted mobile phase flow
• Maximum operating pressure of 3000 psi
• Maximum operating temperature of 80°C
• Typically supplied with 20 µL sample loop
• Excellent chemical resistance to common LC solvents

Advantages of PEEK Construction

The PEEK construction used in the Model 3725I eliminates metal surfaces within the wetted flow path, minimizing analyte adsorption and preventing potential catalytic degradation. This design is particularly beneficial for protein analysis, biomolecule separations, ion chromatography, and trace-metal sensitive workflows.

PEEK materials also offer strong compatibility with common LC solvents such as acetonitrile, methanol, water, and buffered mobile phases, enabling the injector to operate reliably across a broad range of chromatographic conditions.

Injection Methods

The Model 3725I supports both complete loop filling and partial loop filling injection techniques. Complete loop filling ensures highly reproducible injections because the sample loop defines the injected volume, while partial loop filling allows smaller injections when sample availability is limited.

Maintenance and Serviceability

The valve is engineered for long service life with replaceable wear components including the rotor seal and stator face assembly. Maintenance kits are available to restore injector performance and extend operational lifetime.

Typical Applications

The Model 3725I is commonly used in laboratories requiring a biocompatible manual LC injector with electronic position feedback. Typical applications include biopharmaceutical analysis, ion chromatography, environmental testing, and analytical LC research workflows.