Chromatography Forum

I was looking for some information about HPLC columns with sub 2 micron particles, when I came across the following figure on a manufacturer's website (I replaced the column name by a black box):



In the title of the figure is stated: "An exceptionally accurate mean and a tight, symmetrical distribution around 1.9 µm"

Looking at the figure, I indeed see a Gaussian distribution; but having a second look, I noticed that the X-axis is logarithmic !!!!! With a linear scale, the distribution would have a large tale.

Is it normal to display the particle size axis as a logarithmic scale, or is this a piece of very misleading information?

Some newer silica based sub 2 µm particle columns indicate to cause less back pressure. Is this because very small particles are absent? And the presence of (a small quantity of) larger particles has a substantial negative impact on column efficiency?

Logarithmic scales for PSDs are the norm in my experience, but if you note the distribution extends well below 1-um. Presenting results on a volume (rather than number) distribution then claiming no <1 um particles is very misleading. I'm sure a number distribution of particles would show a mean of like 0.7 um (or less).

The standard tools for measuring particle size distribution display the distribution on a logarithmic scale. So there is nothing wrong with that.

That said, this particle size distribution is by no means "tight". It actually is fairly broad, as you have accurately observed. It is way outside the specifications on particle size distribution that I am used to at my company.

I've actually taken apart columns and sized the particles using laser light diffraction backed up with SEM data and found the 'advertising' to be a little misleading.

It's hard to believe that the distribution above has particles down to 0.1um and no further, is this backed up by SEM? You shouldn't always rely on one technique (especially the black box of particle sizing) on characterising particles.