Simulations are indeed very helpful when it comes to understanding the behavior of technical systems.

To represent reality well enough, scientific simulations are often complex and are carried out on mainframes.

We cannot simply show such simulations here. Instead, I would now like to present an interactive website that a group of Professor Michael Engel have created.

The website aims to demonstrate the functionality of a chromatographic column in a very simplified way.

You, as a spectator, now have the opportunity to follow in our footsteps. Here we go.

By entering the address shown here on the screen in the web browser, you get the start page of the simulation tool.

Here is a brief overview first. Click on Start to start.

For level 1, a simple chromatographic column is simulated on the first page.

The chromatographic column is filled with identical red particles.

Let's start the simulation by clicking on the checkbox.

In the simplified representation, the column corresponds to a ball track.

The particles are spheres that are introduced into the column from above.

The balls follow gravity and fall several levels.

In doing so, they collide with each other and with the porous medium.

It relies here by alternating levels.

Since the simulation runs so very slowly, we can accelerate it by setting the speed button to medium.

It's much faster now.

The particles move down like a worm.

The chromatogram is on the right.

The chromatogram is a bar graph.

Individual bars correspond to the transit times of the particles through the marble run.

The height of the bars corresponds to the frequency of the transit times.

Here you can see that most of the particles need around 40 time units to leave the marble run again.

You can also see that a longer simulation improves the statistics.

The fluctuations between individual bars are getting smaller and smaller.

The curves are getting smoother.

It is even faster if we set the speed to fast.

Then the particles use rush dropt.

In our simulation, we want to make sure that the results are sufficiently accurate.

We can say the results are statistically significant.

An additional parameter is affinity of the nanoparticles for the wall.

In the experiment, this describes how much the particles that we want to separate are hindered in their movement through the chromatographic column.

Here, the affinity is implemented as rolling friction of the balls.

If we increase the affinity, the period shifts in the pillar from about 40 units to about 60 units up to about 80 units.

In the next step, two types of particles are introduced in the column.

Red large spheres and green small spheres.

The spheres interact and can block each other.

In principle, we could suppress this effect by decreasing the concentration.

In the experiment, this can be the case.

It is not realized here.

We reach again the faster step.

And then even faster.

Two maxima can now be seen in the experiment. A red one for the red spheres and a green one for the green spheres.

The green particles are clearly a little faster because their retention time is on average a little smaller.

However, we see this difference only when we increase the number of experiments enough, which means when the static effects are sufficiently good.

By increasing the affinity of the red particles, we can slow them down.

The peaks separate further. The separation is improved.

Obviously, we can also reverse the separation. If we increase the affinity of the green small spheres instead.

Here, the peaks are still not completely separated.

It looks like there is a complex interplay between the two types of particles.