ViscoStar: The next generation online differential viscometer.
A highly sensitive, on-line differential viscometer used in conjunction with SEC-MALS-IV to determine the size and conformation of all types of biopolymers, synthetic polymers and even proteins and peptides.
Multiple Novel Technologies
The ViscoStar® incorporates multiple novel technologies to provide the highest sensitivity, stability and solvent compatibility of any available viscometer for GPC. Its ease-of-use and serviceability make it the perfect companion for Wyatt's DAWN® light scattering and Optilab® refractive index detectors.
Another path to polymer and protein characterization: SEC-MALS-IV
When coupled with size-exclusion chromatography and a concentration detector such as the Optilab, the ViscoStar derives the intrinsic viscosity (IV) of polymers. An inherently valuable physico-chemical property in itself, IV is best utilized together with molar mass information from multi-angle light scattering (SEC-MALS-IV) to derive the hydrodynamic radius, conformation, and branching ratio of a macromolecule in solution.
Key benefits of the ViscoStar
- High sensitivity, equivalent to 100 ng of 100 kDa polystyrene in THF at 1.0 mL/min injected onto a standard GPC column
- High dynamic range of over 135,000:1. The full measurement range corresponds to over 13 mg/mL of 100 kDa polystyrene in THF
- Extended solvent compatibility with all-316 stainless steel transducers
- Temperature range from 4 °C to 70 °C for polymers or proteins that require a range of temperatures
- Minimal band broadening thanks to fast pressure transducers
- Pump pulse suppression to below 4 Pa (hardware alone) or 1 Pa (hardware + software) without loss of chromatographic resolution
- Automated capillary bridge tuning with no moving parts, to guarantee a perfectly balanced bridge, every run
- Enhanced thermal stability with drift of <2.5 Pa/hour
SEC-IV without MALS?
Yes, as much as we love MALS for optimal polymer analysis, it's true that there are occasions when it just won't fit the bill.
Universal calibration is a parallel technique to SEC-MALS for determining molecular weight, commonly used to characterize linear polymers. While universal calibration overcomes some of the problematic issues associated with column calibration by reference molecules, it does not account for non-ideal column behavior caused by chemical solute-column interactions or hyperbranching.
Universal calibration is particularly-well suited to replace MALS for:
- Strongly fluorescent polymers, in particular those not adequately addressed by a DAWN with long-wavelength (785 nm) laser or a standard DAWN (685 nm) with fluorescence-blocking filters.
- Weakly-scattering polymer/solvent systems with very low dn/dc values
The Mark-Houwink-Sakurada relationship makes use of empirical relationships between intrinsic viscosity and molar mass, specific to each polymer and solvent, to estimate molar mass from SEC-IV measurements. Of course, the best way to determine MHS coefficients is to measure them using SEC-MALS-IV and ASTRA!
Go to the Advanced Technology tab to learn more about the unique features of the ViscoStar.
Innovations in the ViscoStar
Exquisite sensitivity, stability and robustness require more than just incrementally better engineering. They are made possible by the innovative research and development carried out in Wyatt Technology's R&D center. Here are the primary innovations incorporated in this instrument:
Thermal bridge tuning - The four arms of the bridge must be perfectly balanced in order to make the most sensitive measurements. And yet accumulation of dirt or sample on the capillary walls can skew the balance set during production. Thermal bridge tuning in the ViscoStar accomplishes this balance quickly and robustly, without sliding seals or other mechanical means, guaranteeing perfect balance every run.
Pump pulse compensation - Even a well-balanced bridge is inherently susceptible to systematic noise due to dynamic pressure pulses generated by the chromatography pump. Complete impedance matching symmetrizes the dynamic properties of the capillary bridge and suppresses pump pulses in the DP transducer by 100x. And the ViscoStar does it without introducing the artificial band broadening that is used by other online viscometers to smear out pump pulses at the cost of reduced chromatographic resolution.
Pump pulse elimination - ASTRA® implements a unique algorithm for calculating intrinsic viscosity from the IP and DP transducers that eliminates the contribution of pump pulses in the IP transducer. An additional, proprietary software filter eliminates residual DP pump pulse levels without any loss of resolution.
Dual-Peltier thermal control - Wyatt's ViscoStar is the only online viscometer that offers heating and cooling of the sample via Peltier-based temperature regulation. Its dual-Peltier control eliminates internal temperature gradients, bringing signal drift down to just 2.5 Pa, 50x less than competing instruments.
System pressure protection - The highly sensitive pressure transducers utilized in the ViscoStar must be protected from overpressure due to high flow rates and/or tubing clogs which might occur in the instrument, or even in downstream instruments. The ViscoStar incorporates active protection with a system pressure sensor and bypass valve. Besides offering full protection, this arrangement has the added benefit of providing a positive warning to the user and data logging of protection activation.
The ViscoStar may be used with any* GPC or HPLC-SEC system as long as the sample does not need to be heated above 70 °C in order to flow through 0.010" (0.25 mm) i.d. tubing. Combine with an Optilab for the concentration measurements needed in viscometry calculations.
ASTRA supports Universal Calibration as well as molar mass determination using Mark-Houwink-Sakurada coefficients.
Combine the ViscoStar with a DAWN® or miniDAWN® MALS detector for an even more versatile combination that can determine Mark-Houwink-Sakurada parameters and other measures of conformation and stability. ASTRA handles all the calculations you need for full characterization of your polymers.
*Certain HPLC pumps or injectors generate pressure pulses that can interfere with sensitive differential viscosity measurements. While the ViscoStar overcomes most of these, it is always best to start with a pulsation-free pump. Contact Us for information on optimal GPC systems.
|Sensitivity (minimum detectable sample)||0.1 μg of 100 kDa polystyrene in THF at 1 mL/min, under typical GPC conditions|
|Differential pressure noise||< 0.05 Pa|
|Differential pressure range||6.9 kPa, protected against overpressure|
|Linearity||0.5% of full scale|
|Differential pressure drift||< 2.5 Pa/hr|
|Capillary bridge autobalance||Thermal, leak-free mechanism|
|Sample shear rate||5000 Hz with water at 1 mL/min|
|Max. flow rate||Aqueous: 1.5 mL/min; THF: 3 mL/min|
|Delay volume options||16.2, 10.8 or 5.4 mL, with additional factory-installed option for 32.4 mL1|
|Max. permissible pressure inlet to outlet||690 kPa|
|Wetted Materials||316 stainless steel, PTFE, zirconium silicate, Kalrez®, Inconel, 26-1 Stainless Steel|
|Range||4 ºC to 70 ºC|
|Ambient Range||0 ºC to 40 ºC, 20% to 70% RH|
|Digital Output||20 bits @ 10 Hz|
|Inputs||Autoinject contact closure, Alarm In, Analog In: 2 differential inputs, 18 bits resolution, range -10 V to +10 V|
|Outputs||Autoinject Retransmit, Alarm Out, Recycle Out|
|Front Panel Display||7" (178 mm), high-resolution, multi-touch display for viewing/setting signals, instrument settings and diagnostics.|
|Dimensions||58 cm (L) x 36 cm (W) x 18 cm (H)|
1 Volume of fluid through the ViscoStar until the retained sample elutes. Actual volume of fluid in the column is half this value.
Host PC requirements may be found in Computer Requirements.
Specifications subject to change without notice.
microViscoStar® - Similar to the ViscoStar but designed specifically for use with UHPLC/APC.