RD4: 250-280-RI-Cond

UV, RI and Conductivity Monitor for Preparative liquid chromatography and FPLC

GeneralSpecificationsOptionsSeparation ExamplesFraction RouterUser Manual

Operation mode

Autonomous: all unit functions are controlled from the front panel, so no external PC is needed.

Data presentation

Four real-time graphs (one for each data channel) are plotted on a color LCD.

Light sources

  • 250nm and 280nm UV LEDs, followed by narrow bandpass diffraction filters
  • Spectral bandwidth: 9nm
  • Wavelength accuracy: ± 2nm
  • Current through UV LEDs: ≈ 20% of the maximum allowed for the corresponding UV LED. The operating current reading is available on the detector's screen.
  • Light sources are kept at a constant temperature by a Peltier element to minimize long-term drift
  • Typical lifetime: 15 years of non-stop operation

Flow cell*

  • A single wide-range embedded flow cell is implemented, US patent.
  • Total volume: 150μl
  • Flow rates: 0.1 to 300ml/min, no split - all eluents travel through the flow cell via the same path.
  • Maximum operating pressure: 250 psi (17 bar)
  • Wetted materials: quartz, sapphire, titanium
  • Solvents compatibility: any (except HF; see manual)
  • pH stability (long term): 1-13
  • pH stability (short term): 1-14
  • Hydrodynamic resistance: low, suitable for gravity chromatographic columns

Monitoring of UV absorption at 250 and 280 nm

  • Range: 0.001 – 100* AU (Absorption Units)
  • Resolution: 0.0001 AU
  • Baseline noise: < 0.0001 AU
  • Drift: 3.0 x 10-4 AU/hr at constant temperature
  • Auto-zero: the detector may be zeroed at any time

Monitoring of Refractive index

  • Measurement type: absolute
  • Measuring wavelength: 280nm
  • Range: 1.2000 to 1.7000
  • Resolution: 0.0001
  • Thermally compensated measurements

Monitoring of Conductivity in S/m

  • Two electrodes platinum cell
  • 0.001-15 S/m range

Monitoring of Proton mobility

  • This technology was developed by REACH Devices.
  • Works in any solvent from water to hexanes
    • In aqueous solvents, this channel measures conductivity.
    • In non-aqueous solvents, this channel measures proton mobility: very sensitive for weakly ionic compounds (e.g., allows the user to monitor sugars in dichloromethane).

Data storage

Data is saved automatically to the internal non-volatile memory. The memory can hold a maximum of 131,056 data points.

Acquisition rates (non-stop run times)

  • 5Hz (7 hour 16 min)
  • 2Hz (18 hours 12 min)
  • 1Hz (36 hours)
  • 0.5Hz (72 hours)
  • 0.2Hz (7 days)
  • 0.1Hz (15 days)

Data Transfer

By user's command to USB drive. No data acquisition occurs during the data transfer.

Communication Interface

  • One digital fraction count input from a fraction collector; detector can react to intermittent mechanical contact closure and TTL level signal.
  • 4 independent analog outputs in 0-1V range (see manual for transfer functions), corresponding to (a) UV 250 nm, (b) UV 280 nm, (c) refractive index and (d) conductivity channels. The output (a) can be reassigned by a user to provide data from any other channel (b, c, or d) and used to provide the respective analog signal for contemporary fraction collectors.
  • All input and output channels are galvanically isolated from mains ground and detector's internal circuitry ground for safety and noise resistance.


  • Dimensions: 5.7” diagonally
  • Resolution: QVGA 320x240
  • Back-light: white LED
  • Protection: hermetically covered with 2 mm glass – the assembly is solvent resistant.

Case material

Anodized titanium, covered with 1 micrometer Teflon – complete resistance to any solvent spills.


7.5” x 5.25” x 2.25” (190 x 133 x 57 mm)


3 lb (<1.4 kg)

Power requirements

  • Embedded internal (USA, Asia, and most other regions) or included external (Canada, Europe) power supply
  • Frequency: 50-60Hz
  • Voltage: 90-240V
  • Current rating: 0.1A for 90-120V, or 0.06A for 220-240V; 10W max power draw

*The data is simultaneously collected for optical path-lengths 0.001 to 10 mm, and presented to user “as if” the acquisitions occurred using a 10 mm optical path-length. Unlike other UV monitors, the chromatogram data collected by RD4 detector does not plateau when concentrations of UV-absorbing compounds are high, allowing the user to see true analyte peaks as they leave the column.

Superior performance that outclasses all comparable instruments

The comparison chart of commercially available UV detectors and monitors for liquid chromatography

How to Choose a UV Detector for Chromatography Applications