It was three weeks ago now that we launched the new and expanded Zetasizer Advance range of size, zeta, and molecular weight capable systems. We had a good attendance at the live Webinar, so thanks to all that could attend – we hope you found it useful and enjoyable.
For those that could not attend the live event, a recording of the event can be found here.
At the live event, and subsequently, we have had some good questions come through about the Zetasizer Advance range. We thought we would put this little blog together as a type of FAQ as many of you may also have similar questions. So, without further ado, lets start on the questions…
I am sorry if this was not 100% clear from the launch event. The Advance series consists of three models, Lab, Pro, and Ultra and these are each in two variants – the blue label and red label variants.
The blue label systems are generally equivalent to the outgoing Zetasizer Nano series and will perform extremely well for most sample types, as 17 years of the Nano range being the market-leading DLS/ELS system will attest to. We say that the blue label variants are suitable for most samples that are moderate to strong scattering samples, for instance, lipids, metal oxides, and metallic colloids and may have advantages in so much as it may not be necessary to dilute your samples as much to optimize data quality.
The red label systems provide higher sensitivity for more weakly scattering dilute sample types, for instance, proteins and peptides at a few mg/mL concentration or lower.
You could think of the Ultra as Lab and a Pro in the same box – though in reality, we introduced the Ultra to exploit the capabilities that such an optical arrangement brings, such as Multi-angle dynamic light scattering for higher resolution DLS and very low sample volume, high quality, size measurements. Also on the Ultra-red label the ability to measure per peak particle concentration with no calibration curves required. The Ultra could be said to be greater than the sum of its parts!
No, the upper size range of the Zetasizer Ultra Red (and Blue) is 10um with indicative results above this using extended size analysis and the low volume disposable sizing cell. The 500nm upper limit is for Multi-angle dynamic light scattering (MADLS) measurements for higher resolution DLS measurements and this is also true for Particle Concentration measurements that use MADLS for the improved accuracy and precision required for that type of measurement.
I am sorry to say that it’s not possible due to the different optical arrangements between the Nano 90-degree capable systems and the 90-degree capable Advance systems. The Advance systems are optimised for this new cell-type.
Molecular weight on a batch system, such as the Zetasizer Advance range, will give you an average molecular weight. The Zetasizer Advance range will measure molecular weight from below 1kDa to a theoretical 20MDa. We would expect the average molecular weight of a sample measured on Zetasizer and GPC (or SEC if you prefer) to agree within 10%.
Of course if the molecular weight is of prime importance to you then we would always recommend the use of a GPC/SEC system, such as OMNISEC as they provide molecular weight distribution analysis as well as other parameters and feature-rich analysis not available on a batch system.
I think this question was discussed at the launch event as its quite a common question. But, to recap here. The most recognized theory of colloidal stability, DLVO, is only applicable for systems that are sufficiently dilute that particles are not crowded enough to be in contact or for double layers to start to overlap. There are theories for more concentrated systems but these, to my knowledge, are very much conjectural at present.
But that does not mean for your sample a cloudy sample is not suitable, that depends on the particle size of your sample to some extent. It is probably best to run a series of dilution experiments to determine a region where zeta potential is independent of concentration and measure your samples at that concentration range. Of course, you need to be careful with your diluent choice. The zeta potential of a sample depends on the ionic environment and as such your diluent should match the original continuous phase of your native sample in terms of ionic strength and composition as well as any other dissolved constituents that maybe absorbed or may desorb with dilution. It is often best practice to dilute with the actual continuous phase obtained from centrifugation or filtration, wherever possible.
Well, that concludes the FAQ. Once again, thanks to all that attended or have spent their time watching the recording and a big thanks to Mike Kaszuba for presenting the launch.