I am about to use smaller particles than 5um and I know that the analysis time should be shorter by 2 to 3 times.

My question is:
Does this time saving extend to equilibrating the column to a new mobile phase?

Ummm,
I don't think smaller particles in themselves give shorter retention times, they give better resolution (sharper peaks) and higher back pressure. If you use shorter columns packed with the smaller diameter particles then of course you will get shorter run times, and the reequilibration times for the shorter columns will decrease also.

Regards,
Mark

The plate number of your column increase, so you can use shorter columns with the same plate number as your longer column with larger particles.
The re equilibration times decrease as mentioned above.

One issue: In our company we have lot of trouble with columns with 3.5µm particles. The pressure is getting to high, but we work on it to get the columns work fine.

I found it a good method to save lots of time.

I often work with 3 µm particles.
However, they require shorter columns as the backpressure increases. So with shorter columns and smaller diameters (15 cm / 3 µm instead of 25/5) the retention time will decrease by 40 %. The pressure will increase by 67%! Plate numbers and resolution will be app. the same. With a 10/2 column rt will decrease by 60 %, pressure will increase by 150 %!
If you decrease the flow rate to get the same back pressure as with longer column / bigger particles, you will end up with the same run time. In turn, if one increases flow rate on longer column/bigger particles until back pressure is comparable to shorter column/smaller particle the run time will be again the same.
Considering this, achievable run times depend on the back pressure the system is able to handle. With smaller particles and shorter columns you will need less solvent.
The only way to escape the back pressure dilemma would be a more homogenious particle size distribution. This is certainly a challenge for the stationary phase producers.

Thank you,

Anonymous

to reduce the back pressure u can use column oven. it will reduce the RT and runtime also

to anon 031016 11:26:
Keep in mind that different temperatures can change selectivity

Alex

Here is another tidbit of information: if you scale column length and particle size simultaneously, the maximum plate count that you can get from these columns remains the same. Also the column backpressure for the shortest analysis time remains the same. This means you can't get a shorter analysis from a 10 cm 2 micron column than from a 25 cm 5 micron column. The advantage of the shorter column with the smaller particle is that you get more plates at shorter run times. You can continue this game until you run out of pressure. For a 10 cm 2 micron column, the optimum plate count is achieved at around 3000 psi (200 atm).
All of these statements are correct for any solvent or temperature...

Uwe,

Were can you find these information about which pressure gives the optimum plate count for a given column?

In my book - HPLC-Columns, Theory, Technology, and Practice, Wiley-VCH.

Thanks for giving me the opportunity to advertise...