Chromatography Forum

Hi
There have been many articles on Poroshell/fused core particle/superficially porous particles. Well I would like to know as users what you all feel about “Poroshell/fused core particle/superficially porous particleâ€

I can send to anybody interested a copy of my presentation at last PittCon, where I was invited to talk about this subject. The bottom line is, the Halo particles are 2.7 micron particles, while sub-2-micron particles are sub-2-micron particles. Smaller particles give a higher performance, but require higher pressure.

You may find this article interesting as well:

Journal of chromatography A, 1169 (2007) 125-138
F. Gritti, G. Guiochon

Cadenza CW-C18 is an alternate to fused core technology.
Low surface area (faster elution) and minimal loss in efficiency
at higher flow rates (may also see improved sensitivity at higher flow rate):

http://www.imtaktusa.com/site_media/fil ... TI385E.pdf

Just to put things into perspective: an ACQUITY UPLC 1.7 micron 15 cm column delivers 47 000 plates per column.

A couple of things:

a). The important thing to notice in the data is change in efficiency.
The flow rate for 2mm I.D. was pumped up to 0.6mL / min, and
there was minimal loss in N (<5%). So you get a flat
VD curve with 3um.

b). Cadenza CW-C18 is 300A pore size. Conventional thinking has
been that wide-pore ODS results in poor efficiency for small molecules.
This is incorrect - in fact, a well designed wide-pore ODS is very
useful for small molecule separations.

c). Actual values of N are dependant upon solute, experimental conditions,
ect.

d). Under optimal conditions, Imtakt's 250x4.6mm, 3um generates
50,000 plates. And this can be used on conventional HPLC.
The 150x2mm, sub 2um requires U-HPLC system.

Even then - having all that horsepower is no guarentee one will resolve 2 peaks.

[quote]"Conventional thinking has been that wide-pore ODS results in poor efficiency for small molecules."[/quote]


I have never heard such an idea... Maybe I am not a conventional thinker

However, a 300 A packing has roughly a 3x lower surface area than a 100 A packing, all other things being equal, and thus a roughly 3x lower retention.

Anyway, there is more than just the higher plate number per column length that one can get from sub-2-micron packings. In addition, you always achieve such a high plate number in a shorter time compared to a larger particle. There are two reasons. One is the higher linear velocity that you can use with smaller particles. The van Deemter curve shifts to higher velocity with the smaller particles. The other factor is that to get the same plate number, you only need a shorter column. Therefore a 1.7 micron particle is 4 times faster (for the same plate count) than a 3.5 micron particle. Demonstrated for example in U. D. Neue, „Chromatography: Liquid: Ultra-Performance Liquid Chromatography“, published on-line in: Encyclopedia of Separation Science, Elsevier, 2007.

Therefore a 1.7 micron particle is 4 times faster (for the same plate count) than a 3.5 micron particle. Demonstrated for example in U. D. Neue, „Chromatography: Liquid: Ultra-Performance Liquid Chromatography“, published on-line in: Encyclopedia of Separation Science, Elsevier, 2007.

I won't argue with the math.

But "4X" faster is a lot better than the "U-HPLC is potentially 9X faster than HPLC..."
marketing everyone is accustomed to seeing (comparing 5um vs. sub 2um).

We are in the business of 3um packed silica columns - so we will always point out that
"Potentially 9X faster" is for 5um, and that the difference is MUCH less for HPLC with 3um
columns.

However, a 300 A packing has roughly a 3x lower surface area than a 100 A packing, all other things being equal, and thus a roughly 3x lower retention.

Yes - so if alpha and k' is large, there is an opportunity
to reduce run time by reducing alkyl chain length (or reducing surface area).
So reducing run time does not always require reduced (sub 2um) particle size.

Wow, interesting argument... If I put it to the extreme, it means that if I have nothing to separate, I don't need a column. Who would disagree?

Except for we have lower limits for k' and Rs correct?
We try and have k' > 2 (sometimes > 1 is ok), and Rs > 2

Take for example the separation below:
http://www.imtaktusa.com/site_media/fil ... TI086E.pdf

How can one reduce run time?

Option A: Reduce particle size and length of the C18 phase (sub 2um) and purchase U-HPLC system. (ex: 50x2mm, sub2um, 0.6mL/min).
RESULT - faster run time. The method may still require gradient elution.

Option B: Keep your perfectly good HPLC. Optimize the phase (same particle size, but decrease alkyl chain length from C18 to C8).
(ex: 75x4.6mm, 3um, 1 mL/min)
RESULT - faster run time. The C8 phase may even allow for isocratic elution.

Efficiency should be similar for both methods.

Whichever method / technology works best is up to the end user.

So now after you have done all your homework on a C8 packing with let's say a 3.5 micron particle size, you can translate the exact same separation onto a 2x shorter column with 1.7 micron particles. Now you find that the exact same separation can be done in 1/4 of the time...

Some of us find this to be worthwhile.

I have to admit that short analysis times are not necessarily on everybody's list. There are still a lot of separations in the real world that are run on microBondapak C18, developed in 1973...

Something to consider from the LC-MS point of view. I have heard from several people/companies/contract laboratories that the introduction of UPLC have allowed them to decrease their capital investments in MS equipment as they can now do more analysis (faster etc) with UPLC-MS instead of buying several HPLC-MS systems... the same should stand true for other type of detectors although they cost much less, therefore not having the same benefit...

A reasonable approach would be to pay the premium for new HPLC purchases and move to UPLC but I wouldn't invest in switching existing HPLC to UPLC...

Bryan,

Please don't mix up resolution capacity (plate number) ad selectivity. There are certainly applications in which one can get the same run time and resolution with an old 7µm Type A and a new 3µm or sub 2µm column. But this is just different selectivity.
In method development any additional resolution capacity (plate number) helps especially if the number of peaks rises and unknown peaks a likely to occur.
I still prefer 3µm columns as suitable equipment is readily available (quaternary pumps, column switching valves) and they will also work on our old workhorses.

Kostas, replacing several old HPLCs with a single UPLC with higher throughput sounds promising but:
in case of different applications one would need a column / solvent switcher
in case of any issues everything is down
some people prefers for some reasons dedicated devices for some applications.

Alex

Kostas, you're right to raise LC-MS; for those of us with old-fashioned, slow-scanning MS systems, UPLC is rather a non-issue.

Alex -

Thank you for your response. I updated my comments.

All I wanted to say is you can sometimes decrease run time by
changing column selectivity. Reducing particle size is not the only way.