AF4-UV-MALS size distribution evaluations of iron oxide nanoparticle samples (IONP) - Retention time approaches

This dataset presents AF4-UV-MALS size measurements of iron oxide nanoparticle.
The nanoparticles were synthetized by BAM and measured at SMD (and also at LNE, data not included here).
The small size of the sample (~10 nm) makes the measurement by MALS (inline of AF4) very challenging: weak signal, and almost not size information. AF4 has the advantage of having a theoretical description. Elution time relates directly to hydrodynamical size (working principle of the method). This leads to other sizing methods (size distribution measurement methods, actually), based on extrapolation of external calibration (with several size standard, relating size to elution time) but also taking advantage of the theory (single parameter to calibrate: effective channel thickness) in its linear model, in isocratic mode, which admit a mathematical analytical closed form. The flow program here developed is isocratic in the beginning of the run, where the sample is fully fractionated. 

This dataset shows that size distribution measurement can be more efficient using retention time, when detector reach their limits, for example, ~sizes <20 nm (order of magnitude - sample dependent) are difficult to measure with MALS.
Application of the theory is also shown to be more versatile with respect to size standards samples and sample to be analyzed: flows can be adjusted to better suit optimal separation conditions (flow program) of each of the samples. 
On the other hand, external calibration (curve), is limited to application of exactly the same flow program.

The model here applied follows the following equation :
$$ d= 2 \frac{t_r}{w_{eff}^2} \frac{k_B T}{\pi \eta} \left(1/\ln\left(1+\frac{\dot{V}_x}{\dot{V}_d}\frac{A(z)}{A_{tot}}\right)\right)$$
that can be found in the following references :

• 10.1016/j.chroma.2012.07.029
• 10.1021/ac00052a025
• 10.1021/ac00010a013