Yesterday we launched the Viscotek SEC-MALS 20, a new modular multi-angle light scattering detector.  The Viscotek SEC-MALS 20 is an addition to the Viscotek range of GPC/SEC (Gel Permeation Chromatography/Size Exclusion Chromatography) systems and detectors for the measurement of molecular weight and size (Rg) of proteins, as well as natural and synthetic polymers.

We explained how this new MALS detector has new optics designed to maximize measurement quality and certainty and we looked at some of the early applications the system has been used for.

Click here to see the launch presentation of the Viscotek SEC-MALS

The application notes we discussed are all now available on the web site and can be found by visiting the SEC-MALS homepage:

Thanks for all those who attended the presentations, and we hope you enjoyed them and the video.  If you would like another view of the video please click the following link:

Your questions made for an interesting discussion afterwards.  We are sorry that we didn’t manage to answer everyone’s questions at the end so we thought we would write them down and publish them in the blog for all to see.  Have a look through them and if you have any more questions, please don’t hesitate to get in contact with us.

Question Answer
What is the minimum Rg available? ­We have set the instrument specification at 10nm but of course it is both sample and conditions dependent.  There is a technical note which describes exactly how we arrived at the 10nm figure called “Sample measurements to demonstrate the specification of the Viscotek SEC-MALS 20”
What is the upper limit in MW?  We are interested in very high MW polymers – 12 to 14 million Da.?The largest single sample we’ve measured so far had a Mw of about 4.5 million Da but was polydisperse with molecules up to about 15 million and down to 500,000 Da.  The system could probably measure higher but this is dependent on the separation more than the system at these kinds of molecular weights.So samples of 12 – 14 million Da shouldn’t be a problem if the chromatography is OK.
­How do you calibrate the MALS? ­The SEC-MALS 20 is calibrated in the same way as all MALS detectors and in fact all static light scattering detectors, by introducing a sample of known scattering or molecular weight into the cell.  We’ve always believed that the best calibration is done with a molecular weight standard as this allows calibration of all the other the detector response factors (e.g. RI, UV) as well as the inter-detector delays and band-broadening all in a single step.  For more information on calibration, please read our white paper, “Static light scattering for GPC/SEC technologies explained”
­Did I hear that this MALS detector can be attached to any SEC inst – Agilent or Waters? How is the resolution when a UPLC column is used? ­Yes, the SEC-MALS 20 can be connected to most SEC systems as long as they are in good working condition and the UV or RI detector has an analogue output to connect up.The resolution with a UPLC column will, of course, be dependent on the exact conditions and sample type.  If you would like to get in touch directly we can discuss in detail.
Can the IV vs. Mw data, through the Mark-Howink coefficient, be used to characterize the degree of branching with traditional synthetic polymers? ­Yes absolutely.  This has been available for a number of years in OmniSEC.
Which Model/Method does the software used to calculate the molecular weight and Rg?  Is there a model for calculate the size of solid particle­?We have the option to use Zimm, Berry or Debye models with 1st to 5th order fits.Currently there is not an option to calculate size for a solid particle.
­Does application note explain why refractive index is not needed?Just to clarify this point, the mobile phase refractive index is still required to calculate sample molecular weight.However the vertical design of the flow cell means that the actual scattering angle does not need to be calculated based on the refractive index of the mobile phase.  The reason is that the scattering angles are the same in all mobile phases no matter the refractive index.  Furthermore, one flow cell is compatible and suitable for all mobile phases so it never needs to be replaced.This is best explained in the technical note explaining the advantages of this new design called “Technical benefits of the Viscotek SEC-MALS 20”
­How does the software deal with radial broadening between concentration and LS detectors? ­The OmniSEC software has band broadening corrections that are calculated during calibration.  These are then applied to samples to account for the broadening of any peaks in the different detectors.  These corrections have been in OmniSEC and our earlier software packages for many  years and have shown themselves to be very reliable.
What about solvent compatibility?The SEC-MALS 20 has no problem working with all the common SEC buffers or solvents.
The video mentions the angles are displayed in the software – what does this mean?With older designs of MALS the data is displayed with only a detector number as the actual scattering angle will change with a change in the buffer refractive index, say when there is more salt in it.  In the new SEC-MALS 20, the angles are fixed around the vertical flow cell so the absolute scattering angles are always known.
Can I connect the SEC-MALS with other detectors – I have a Viscotek system at present?Yes, the SEC-MALS will work with any of the Viscotek or Zetasizer SEC detectors from Malvern, and will work with any RI and UV from other manufacturers – providing they have an analogue output.