In a previous post, I described how you can determine the composition of a sample through GPC/SEC analysis. This powerful method has found many applications, with a recent example being AAV characterization. With these types of analyses becoming increasingly popular, we’re pleased to announce that compositional analysis is now possible with OMNISEC!

Check out the video demonstration below and read on for more information and new features!

What’s in a name?

You might know the compositional analysis method by another name.  In the OmniSEC v5 software platform, we’ve used both “copolymer analysis” and “conjugate analysis” to describe this method depending on the user’s application.  When developing the method for the OMNISEC system and OMNISEC v10+ software, we opted to go with the all-encompassing “compositional analysis” name.

What is it?

Compositional analysis uses both refractive index (RI) and UV detectors to obtain concentration information about a sample’s components. If the sample contains two components that exhibit different absorbances at a given wavelength, like a protein-PEG conjugate, then the relative concentration of each can be calculated using the equations below.

compositional analysis equations

It’s like in algebra when solving a system of two equations for x and y. You can solve for both variables (concentration of protein/A and concentration of PEG/B) because you have two equations (concentration profile from the RI detector and concentration profile from the UV detector). The protein-PEG conjugate example is convenient because the protein is UV active while the PEG is not. Therefore, the RI detector will respond to both the protein and the PEG while the UV detector will respond only to the protein. Please note that for compositional analysis to work, at least one component must be UV-active!

How will it work with OMNISEC?

To perform a compositional analysis with OMNISEC you’ll need to ensure you have the following things ready:

To ensure your system is ready, enter your license in the software by going to File > Options. Then, under the Licensing section, choose Compositional Analysis and enter your code in the field, as shown below.

New features!

You might be thinking, this is perfect to characterize AAVs or ADCs! We agree! That’s why we’ve included application specific results such as Full, Empty, and Total AAV Titers and can provide % Full AAV. The cp/vg ratio is also conveniently calculated based these values. And for those of you working with ADCs, the drug-to-antibody ratio (DAR) can be reported, making it easy for you to confirm that your drug loading is just right.

Final thoughts

In conclusion, the addition of compositional analysis expands the capabilities of OMNISEC. Whether you’re working with novel copolymers or within gene therapy development, compositional analysis offers unparalleled characterization of your samples. Furthermore, if you have any questions please don’t hesitate to contact us or email me directly at

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