RD4-pH: 250-280-pH-Cond, Industrial

Industrial Capacity UV, pH and Conductivity Monitor and Controller for liquid chromatography

GeneralSpecificationsOptionsFraction 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

Combined UV/Conductivity flow cell

  • A single wide-range embedded flow cell is implemented, patent pending.
  • Total volume: 400μl
  • Flow rates: 0.1 to 1500ml/min, no split - all eluents travel through the flow cell via the same path.
  • Maximum operating pressure: 2500 psi (17 bar)
  • Wetted materials: sapphire, titanium
  • Solvents compatibility: any (except HF; see manual)
  • pH stability (long term): 1-13
  • pH stability (short term): 1-14
  • Hydrodynamic resistance: 4 psi backpressure at 1.5 l/min for water at 25 oC

pH Flow cell

  • Total volume: 500μl
  • Flow rates: 0.1 to 1500ml/min, no split
  • Maximum operating pressure: 5 psi with the actual pH electrode, 15 psi with the dummy electrode
  • Wetted materials: stainless 316, Viton, PEEK
  • Solvents compatibility is limited by the pH electrode
  • Hydrodynamic resistance: 3 psi backpressure at 1.5 l/min for water at 25 oC

Monitoring of UV absorption at 250 and 280 nm

  • Range: 0.001 – 100* AU (Absorption Units)
  • Resolution: 0.0001 AU
  • Baseline noise: < 0.0002 AU
  • Drift: 3.0 x 10-4 AU/hr at constant temperature
  • Auto-zero: the detector may be zeroed at any time

Monitoring pH

  • Electrical connector: BNC
  • Input current: <1pA
  • Input voltage range -1500 to +1500 mV, will accept any type of potentiometric pH or Ion Selective electrode
  • Electrode resistance measurement range: 1-5000 MOhm

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 262128 data points.

Acquisition rates (non-stop run times)

  • 5Hz (14 hours 33 min)
  • 2Hz (36 hours 24 min)
  • 1Hz (72 h)
  • 0.5Hz (145 h)
  • 0.2Hz (15 days)
  • 0.1Hz (30 days)

Data Transfer

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

Communication Interface

  • In the field firmware upgrade
  • Up to two relays which can be set by the user to react on change in UV absorbtion, pH or conductivity. Allows for direct or reverse control with hysteresis.(250VAC 4A max)
  • One digital fraction count input from a fraction collector; detector can react to intermittent mechanical contact closure and TTL level signal.
  • Two digital outputs which can be programmed by REACH Devices as requested by the user
  • 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.


9” x 5.25” x 5” (190 x 133 x 127 mm)


4 lb (<1.8 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 1 mm, and presented to user “as if” the acquisitions occurred using a 1 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