HPLc Column theoratical plates

[Chandresh K. Soni]

i purchase one HPLC column and i got the Column performance report with this column.
when i checked this column performance report with same as MOA mentioned on this i am getting 60% less theoratical plates then what is claimed. all the other factors like resolution capacity factor is ok.
when i discussed with vendor they mentioned about column void volumn, mobile phase and column temp.
Now my question is how much % of these parameters will reflect on the theoratical plates (is it reduced by more than 60%).
One more is if i am getting in all other column from many vendor as well as from same vendor another columns plate count is near about 10% variation than why in particular this column i am getting more than 60% less.
One of technical supporter of this vendor communicates that The report is not provided to compare the plate counts (than why this Column performance report is shipped along with the column).

[Gerhard Kratz]

Column Performance report - you mean Certificate of analysis???
If as standard 30.000 theoretical plates per meter are normal and you get only 12.000 plates than please ask to exchange the column from your vendor.
Normally good manufacturers state a little bit lower N than they can achieve in the specifications of a column. Variations with N should be below 5%.
Technical support of your column vendor told you something about column void volume????? Please ask them if they are sure that the column is well packed at 100%. I guess it is not an original manufacturer who sold the column to you. A repacker?

[HPLCaddict]

AFAIK column manufacturers usually run their perfomance tests on optimized HPLCs, i.e. HPLCs with low system volume in order to obtain high plate counts - it just looks better on the certificate and they can boast with their columns high efficiencies.
Depending on the system you are using to retest the column, you may find considerably less plates if your HPLCs system volume is much higher than the original one. This is more pronounced if the column volume is small - you'd need a much more optimized system with a 50x2mm or even 50x3mm column than with a 250x4.6mm column. That's probably why the vendor said something about column void volume - I'd suppose they meant the column volume in relation to the system volume.
Is the column in question a rather small one? If it's something like 50x2mm, I'd be not surprised to loose 60% efficiency on a conventional non-optimized HPLC. If it's something more in the range of 100x4.6 or larger, I'd be concerned...

[bunnahabhain]

I agree with HPLCaddict.
Try to omptimize your system as well: Use narrrower ID tubing, lower injection volume (0.1 µL if your injector can do), look at your flow cell. If you have a 11 or 15 µL flow cell together with a 50x2 mm column, you will end up in really broad peaks and subsequently low plate counts. If you really intend to work with such small columns, you should consider investing in a nano flow cell.

[carlo.annaratone]

Agree with posts above... we need more detail to better discuss the case!

[DJ]

The point of the QA is not so much to boast about what the column can do. The idea to show what the column can do under its optimal conditions. When the column is tested under its optimal conditions, it becomes more sensitive to smaller changes in performance. Otherwise, it would be like testing a formula 1 car on a gravel track.

There are also many ways to calculate N. Use the same formula used on the Q of A sheet.

Lastly, as others have said, use the shortest possible length red peek tubing with freshly trimmed ends and seated ferrules for all connections

Note the column oven temperature on the C of A and match it. Use the smallest possible sample volume.

Post of a picture of the chromatogram here.

[danko]

Guys, try reading the additional note from Chandresh K. Soni (below).

One more is if i am getting in all other column from many vendor as well as from same vendor another columns plate count is near about 10% variation than why in particular this column i am getting more than 60% less.

Best Regards

[bunnahabhain]

As long as the OP does not tell more details about column sizes (maybe the column in question is really a 50x2 mm sub 3-µm one, compared to 4.6x250 5 µm columns which are OK without much tuning) we have no chance to find out what is wrong.

[danko]

It’s almost obvious that Chandresh K. Soni has purchased another one of previously utilized columns and tested it just like he did with the other ones.

Best Regrds

[HPLCaddict]

One more is if i am getting in all other column from many vendor as well as from same vendor another columns plate count is near about 10% variation than why in particular this column i am getting more than 60% less.
.

Is it really that obvious? I cannot see that he had a well performing column of the exactly same kind before...anyway, he will tell us, I hope.

[sga]

From what I understand Soni has bought the "same" column from different vendors. One of these columns appears to be misbehaving.

In that case, I would simply ask for a replacement. I don't see why there should be a variability in the performance of columns.

Soni, can you please name the column ?

[Chandresh K. Soni]

thanks to all of you to guide me now my dealer(agilent) is ready for replacement. the column is Zorbax XDB C18, 75cm and 2.7µm.
actually the question comes b'use when i discussed this issue with vendor they are communicated for all the points to prove that there is no mistakes in the column.

again thanks to all of you.