Comparison of Kinetex and Acquity columns

[Mattias]

I thought this might be interesting...

Direct comparison of Acquity BEH C18 (1.7 µm) and Kinetex C18 (1.7 µm):

Analysed the same day on the same instrument, using the same sample and mobile phase:
Instrument: Waters Acquity
Mobile phase: 20% acetonitrile in 5 mM acetate buffer pH 4.5 (isocratic)
Sample: 20 µl of a 100 µg/ml solution (in-house peptide)
Flow: 0.5 ml/min
Temp: 70C
Column dimensions: 2.1x150 mm

Pressure:
Acquity column: 9400 psi
Kinetex column: 8400 psi
(I am surprised that the pressure difference is not bigger. I thought the core-shell technology would make a larger difference in back pressure!)

Retention time
Acquity column: 18 minutes
Kinetex column: 14 minutes
(More retention on the Waters column, maybe not so surprising)

Tailing factor
Acquity column: 1.7
Kinetex column: 1.4
(clearly better symmetry on the Kinetex column)

Plate count
Acquity column: 12.000 plates
Kinetex column: 16.000 plates
(I am a bit shocked that the Kinetex column gave so much better efficiency. I may have overloaded the Acquity column, giving a lower plate count and more assymmetry)

Conclusion: The Kinetex and Acquity columns are probably comparable. The Kinetex column appears to have a better loadability than the Acquity column. The back pressure was quite similar of the two columns, which means that the Kinetex column (1.7 µm) must be used on a UPLC or UHPLC system.

Feel free to comment!

[MatthewArnold]

Thanks for the info!

A couple of comments:

Pressure:
Kinetex is marketed as a way to reduce backpressure. It's not suggesting that a core-shell particle of the same size will give you a lower backpressure, but rather that you can use a larger particle size and get the same efficiency. For example, a 2.6um Kinetex columns has been shown to have the same efficiency as a 1.7um fully porous particle. So you can swap out a 1.7um fully porous for a 2.6um core-shell and get a ~60% drop in backpressure. This allows you to run at higher flow rates, or just put less wear and tear on your machine. The decrease in backpressure you demonstrated might be due to particle size distribution or a number of other factors.

Retention time:
This is due to differences in carbon load. Retention based on hydrophobicity can be predicted and measured based on the % of stationary phase made up of carbon. BEH C18 has a carbon load of 17%, and Kinetex C18 is at 12%.

Tailing factor and plate count:
This is where the added efficiency of core-shell particles shines. Theoretically, a 1.7um core-shell column should have ~20% more plates than an identical fully porous column. You've demonstrated a higher increase, which can be due to a number of other factors.

Loadability is primarily determined by effective surface area. The surface area of Kinetex C18 is 200m2/g, and that of the BEH C18 is 185m2/g. Indeed, you may have slightly overloaded both columns. As a general rule, the injection volume should be 10uL or less for any Kinetex 1.7um column. It would be interesting to see your results with a smaller injection volume!

[atus]

I did a comparsion with 4 synthetic peptides on an ACQUITY system with both Kinetex and BEH columns. I saw all 4 peptides with the BEH column, but only saw the first 2 peptides on the Kinetex column. Curious enough, the first 2 peptides have MW <2,000, but the last 2 peptides have MW >4,000. I suspect the difference is related to the pore size. Otherwise, similar observation for the detected 2 (slightly better efficiency and a bit lower column back pressure).

[Gaetan Glauser]

Interesting topic. To add some data to it, some time ago, we made a comparison on some small molecules in isocratic between:

1. Waters BEH C18 2.1x100mm, 1.7um
2. Waters BEH RP18 Shield 2.1x100mm, 1.7um
3. Kinetex C18, 3.0x100mm, 2.6um (we adapted the injection volume and flow rate)

The efficiency for BEH C18 and Kinetex was similar, about 20'000 plates. However, the RP18 Shield gave N=30'000. The h constant seemed thus lower for the Shield than the classical BEH C18.

The pressure for the Kinetex was quite reduced (40%-50% if I remember well).

[Abdul]

I think the results would be different if we increased the pH value for the mobile phase

[unmgvar]

Atus,
you are correct in your logic
kinetex columns for small molecules are 100A pores size
the BEH is either 130A or 300A
the 130A can very well do with a 4000 or 6000 da peptide
for kinetex this is border more then border line
i have seen several colleagues that have developed peptide maps with those columns just to be disappointed
very poor stability of the chromatography
very poor life time of the column with use of TFA
but there are other possibilities from halo/ascentis, vyadac, agilent, thermo, chromanik
in most cases the pores are 120A which handles better small peptides and now also new types are out with 160 and higher pores to handle the bigger peptides and proteins

[adam]

When you say that you only saw two peaks on the kinetex, do you mean that the other two peaks seemed to come out in the void, or did you not see them at all.

The latter case would be puzzling. Usually, if the pores are too small the result is early eluting peaks (because if the analytes can't access the pores, they can't interact with the majority of the stationary phase) or broad peaks (which occurs when the analytes can access the pores but the movement is restricted).

It is strange that peaks would dissapear entirely. I guess it must be irreversible adsorption to the column, but this seems unusual to me (especially for fairly small peptides).

Has anyone had similar experiences?