Optilab, refractometer

Universal Detection for Chromatography and FFF Separations

Independent of Chromaphores

Independent of chromaphores or fluorophores, differential Refractive Index (dRI) detectors serve as accurate and versatile concentration detectors in all types of solvents. dRI is part of standard instrumentation for a variety of macromolecular characterization techniques including standard chromatography, SEC-MALS, FFF-MALS and CG-MALS.

Unique dRI Detector

The Optilab® is a unique dRI detector for standard HPLC/GPC with 256 times the detection power and 50 times the dynamic range of every other RI detector for chromatography in existence today, making it a valuable addition to any MALS setup.

Using a combination of cutting-edge semiconductor photodiode technology and proprietary computer algorithms, the Optilab achieves an unprecedented combination of sensitivity and range. These features mean that it addresses both standard chromatographic applications and some challenges unique to light scattering measurements such as high concentrations, determination of sample refractive increments (dn/dc) and solvent refractive index.

Key Benefits

  • Extraordinary dRI measurement range, -0.0047 to +0.0047 RIU (comparable to 25 mg/mL protein in PBS)
  • Highly sensitive, ±7.5 x 10-10 RIU across the entire measurement range
  • Measures solvent absolute refractive index, required for MALS calculations
  • Measures at the same wavelength as the MALS detector, for maximum accuracy in MALS calculations
  • Band broadening < 20 µL preserves SEC resolution
  • Temperature range 4 °C to 65 °C for proteins and polymers that require a range of temperatures
  • High-resolution, touch-screen front panel displays data graphs and diagnostics, even with the host computer turned off

Unparalleled Features

Even though the Optilab offers a dRI measurement range orders of magnitude beyond that of other dRI detectors, unlike other detectors there are no range or gain settings in the Optilab. The full range of instrument detection is always present, and the full sensitivity exists over the entire range.

The Optilab can also do something no other on-line refractive index detector can: it can measure the absolute refractive index of a solution. In addition, it can measure the dn/dc of a solvent at the same wavelength of light as the light scattering instrument. And just to make sure it can't be matched, you can replace the light source in the Optilab for other wavelengths (e.g., 690, 633, 488, etc.) in just minutes!

The Optilab can go below ambient temperatures as easily as above ambient. No hassle temperature control can be programmed from 4 °C to 65 °C. Compatible with all HPLC systems.

Revolutionary dRI detection optics

The Optilab incorporates the breakthrough optical design of the award-winning Optilab dRI detector which makes use of a 512-element diode array and proprietary algorithms, instead of the usual bi-cell design, bringing dRI detection into the 21st century. Later Optilab models added improvements in optical stability, temperature control, LED light source intensity and increased on-board computing power in order to enhance sensitivity and extend the temperature range over the Optilab.

Minimal loss of resolution

Each detector downstream of SEC or FFF adds band broadening and dispersion, according to its internal fluidic volume. With a total flow cell volume of only 7.4 µL — 25% less than the leading HPLC refractometers – the Optilab does not impact SEC resolution adversely. This translates into minimized band broadening and better temperature stability.


An Optilab is generally combined with a DAWN® or miniDAWN® MALS detector for analysis of molar mass / molecular weight, conformation and conjugation of macromolecules in solution by means of SEC-MALS or FFF-MALS. It also combines with a ViscoStar® differential viscometer for analysis of intrinsic viscosity.

General Use

Though its optimal use is in conjunction with MALS analysis, the Optilab can be operated downstream of any standard GPC or HPLC system. While ASTRA® utilizes its 22+-bit digital signal, it also offers a 18-bit analog output for use with 3rd-party systems, typically when MALS is not utilized.

The Optilab offers an unparalleled dynamic range for use as both an online and batch measurement system. For batch measurement, sample is injected into the instrument (usually by means of a WISH Injection Module or Calypso®) in order to measure dn/dc or as part of a CG-MALS interaction analysis.

High Concentration Option

When the primary analysis desired is batch mode, the High Concentration version of the Optilab is optimal since it extends the range of measurement by sevenfold compared to a standard Optilab, while losing only a factor of 2 in sensitivity. The High Concentration Optilab offers measurements up to 180 mg/mL of protein but may still be used in chromatography mode for 99% of all SEC-MALS and FFF-MALS measurements.

Differential Refractive Index
Standard Optilab
   Range -0.0047 to +0.0047 RIU
   Peak-to-peak noise * ± 7.5 x 10-10 RIU
High Concentration Option
   Range -0.0026 to +0.034 RIU
   Peak-to-peak noise * ± 1.5 x 10-9 RIU
Absolute Refractive Index
   Range 1.2 to 1.8 RIU
   Sensitivity 0.002 RIU
   Band Broadening ** < 20 µL
   Flow cell 7.4 µL
   Inlet tubing (0.010" ID) 44 µL
   Outlet tubing (0.030" ID) 370 µL
   Back pressure created at inlet port <50 psi (3.5 bar) @ 0.5 mL/min of pure water, 20°C
   Maximum permissible back pressure at    outlet port 30 psi (2 bar)
   Wetted Materials 316 stainless steel, PTFE, fused silica
Dynamic Range 22+ bits only via digital communication
Data Acquisition Period 0.2 to 10 samples/second
Light Source 660 nm standard; other wavelengths available
Sample Temperature
   Control Range 4°C to 65°C, temperature regulated
   Temperature Regulation ± 0.005°C
Safety Sensors Vapor and liquid (leak)
Digital Output 22+ bits @ 10 Hz
Analog Output ± 10 V or ± 1 V output, 18 bits resolution
Computer Interface Ethernet
   Front Panel Display 162.5 mm, 16-bit, high resolution touch screen displays signal graphs, instrument settings and diagnostics
Auxiliary I/O
   Inputs Analog In (16 bits, ± 10 V A/D), Zero dRI, Purge, Recycle In, Autoinject in, Alarm In
   Ouputs Analog Out (18 bit dRI data), Autoinject Retransmit, Alarm Out, Recycle Out (to switch Orbit between waste and recycle)
Dimensions 58 cm (L) x 36 cm (W) x 18 cm (H)

* Short term peak-to-peak noise is measured as per ASTM-E1303-95(2000) using a 0.5 s collection interval (1-s time constant) and temperature set to 25°C.

** Peak broadening measured over full width at half max, flow rate = 0.3 mL/min.

Host PC requirements may be found in Computer Requirements.

Specifications subject to change without notice.

Other Refractive Index Detectors

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microOptilab - The first RI detector specifically designed for use with all UHPLC systems.