Wyatt Technology offers microViscoStar™, an on-line differential viscometer with high sensitivity. This instrument can be used with SEC-MALS-IV to establish the conformation and size of peptides, proteins, and polymers isolated by UHPLC.
Integrated with various innovative technologies, the microViscoStar™ offers the highest solvent compatibility, stability, and sensitivity of any commercially available viscometer meant for UHPLC.
The instrument’s serviceability and ease of use makes it an ideal companion for Wyatt’s microOptilab™ refractive index detector and microDAWN™ light scattering detector designed for UHPLC.
Another Path to Polymer and Protein Characterization: SEC-MALS-IV
When the microViscoStar™ is combined with a compatible concentration detector like the Optilab UT-rEX and also with UHPLC size-exclusion chromatography, it can derive the polymers’ intrinsic viscosity (IV) quickly but without consuming significant amounts of samples and solvents.
Intrinsic viscosity is an inherently valuable physicochemical characteristic in itself. It can be optimally used along with the molar mass data obtained from a µDAWN multi-angle light scattering (SEC-MALS-IV) to derive the branching ratio, conformation, and hydrodynamic radius of a macromolecule suspended in solution.
Key Benefits of the microViscoStar™
- A high dynamic range of more than 135,000:1; the entire measurement range is equivalent to more than 13 mg/mL of 100 kDa polystyrene in THF
- Excellent sensitivity — corresponds to 5 ng of 100 kDa polystyrene in THF at 1.0 mL/minute when injected onto a standard GPC column
- Temperature range between 4 °C and 70 °C for proteins or polymers that need a temperature range
- Extended solvent compatibility with all types of 316 stainless steel transducers
- Fast pressure transducers enable minimal band broadening
- Improved thermal stability with a drift of < 1.25 Pa per hour
- Automated capillary bridge adjustment without any moving part, to ensure a seamlessly balanced bridge, every run
- Pump pulse suppression to less than 1 Pa (software + hardware) or 4 Pa (hardware alone) without loss of chromatographic resolution
SEC-IV without MALS?
Despite the fact that MALS enables optimal polymer analysis, there are occasions when it simply does not suit the requirement.
Universal calibration — a parallel method to SEC-MALS for establishing molecular weight — is often used for characterizing linear polymers. Although this method can resolve some of the major concerns related to column calibration through reference molecules, it does not consider non-ideal column behavior induced by hyperbranching or interactions between chemical solute and column.
In particular, universal calibration offers a suitable solution to replace MALS for:
- Weakly-scattering polymer and solvent systems that have extremely low dn/dc values
- Strongly fluorescent polymers
The Mark-Houwink-Sakurada relationship leverages empirical relationships between molar mass and IV, specific to each solvent and polymer, to determine the molar mass from SEC-IV measurements. Obviously, the most optimal way to find out MHS coefficients is to measure them using ASTRA and SEC-MALS-IV.
Patented pulse compensation technology in the microViscoStar eliminates pump fluctuations. At the hardware level, the bridge is impedance-matched for dynamic balance, greatly reducing the effect of pump pulses. An additional layer of software filtering eliminates residual pump pulses.
The microVisoStar maintains the narrow peaks and excellent resolution of UHPLC with maximum sensitivity. In this graph, the refractive index and specific viscosity chromatograms of an epoxy resin are overlaid with the molar mass and intrinsic viscosity results calculated from MALS and specific viscosity data, respectively, at each elution volume. The sample was separated on four Waters® APC XT columns in series with pore sizes of 45, 125, 450 and 900 Å.