Chromatography Forum

Hm, . . . that reminds me of a statement made earlier:

Posted: Thu Aug 06, 2009 10:23 am Post subject:
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SiliCycle, is it fair to say that your 30 years of experience put you in a position to know very well how to optimize conditions for your columns, which means that those conditions are usually not optiml for columns of the competition.

in

viewtopic.php?t=11057&start=15

It is just because I worked for Waters for many years and I was HPLC consultant for some other big supplier in HPLC that I cannot say for now. Believe-me supplier of HPLC column are not perfect. If you have a chance, take off the packing of your HPLC columns and look SEM data, you will be very surprise.

listen, this is going nowhere

"SiliCycle, is it fair to say that your 30 years of experience put you in a position to know very well how to optimize conditions for your columns, which means that those conditions are usually not optiml for columns of the competition. " - is just an opinion that no one has to believe in

"Believe-me supplier of HPLC column are not perfect. If you have a chance, take off the packing of your HPLC columns and look SEM data, you will be very surprise." - is the same as above

lets talk results and facts, and if not then why even open one's mouth?

Absolutely true it's not going somewhere. I don't need to prove anything here, I know it's tough for you guys. So I closed the discussion.
Good Luck

Absolutely true it's not going somewhere. I don't need to prove anything here, I know it's tough for you guys. So I closed the discussion.
Good Luck

Hello All....

Why are we all becoming emotional ? Lets look at the discussions based on proven merits !! Age / experience are just weights which can give credence if supported with facts .

With time the processes which were bottleneck are addressed and let us admit it , Is there a best any time (all the time ) .....reality is one can be best till the time some one comes up with a better !

Column chemistries ( specially C -18 ) have changed so much , the best have all been replaced by even better column chemistry modifications !!

Let us keep looking for more ! keep discussing ....

Cheers !!

grzesiek, you might be justified in claiming that it is an opinion that experience might allow someone to be skilful in optimizing a column, but is it opinion to point out that optimal conditions for one column of a certain type might not be optimal for all columns of this type by all manufacturers? Is it opinion to hint at the fact that some columns of a certain type are best for a certain problem others for another separation problem?

Mayank72, it seems that columns have mostly been complimented with columns of differnt chemistry, not all replaced, luckily.

If we can send the message to manufacturers that columns of the same type, but with different chemistries are welcome then this discussion has gone somewhere useful, even though it swerved way off the original question.

"which means that those conditions are usually not optiml for columns of the competition." - I would not agree with that at all, there's no logic in it, It can mean that and it also can be the oposite

"optimal conditions for one column of a certain type might not be optimal for all columns of this type by all manufacturers?" - well because of the word might I really might agree with this statement

you see, the words you use and the way you use them are both in fact important

One of a critical aspect of our application involves:

injecting a suspension directly onto the hplc column:

Silicycle might have an advantage over Zorbax in that their pore sixe is larger than that of the Zorbax columns.

Does having this greater pore size provide some relief in backpressure and/or provide a optimal path for a direct suspension injection?

I wonder ......

wide pore would have lower surface and so retention, I wouldn,t expect pressure relief

maybe you'll read about monolithic columns for direct injection of suspension, this can be interestiong to you

The pore sizes of packings are designed with the applications in mind. A pore size of 100 Angstroem is sufficient for analytes up to small peptides, and provides optimal retention. For peptides and small proteins, larger pore sizes are used, due to restricted access to the pores for such larger molecules. Restricted access means lower performance, and thus one compromises retention and chooses the larger-pore packing for peptides, proteins and related applications. A large pore volume is actually a disadvantage, since pore volume is wasted space in the column, and you loose retention with a larger pore volume. This is different from a monolith, where one looses retention, but gains in permeability. With a packing with a very large pore volume, one looses surface area, but gains nothing. The other thing about a very large pore volume is the lack of strength of the silica.
If one knows the pore size and the specific surface area, one can estimate the pore volume. This is what I did, and based on the information that I got, I estimated the pore volume for the Silicycle packing to be around 2 mL/g, while the Zorbax packings tend to have a pore volume around 0.5 mL/g.

This "end-capped ODS phase that also has low pH durability" issue was solved a long time ago.

- Conventional silica ODS (narrow pH range): monofunctional ODS + TMS endcapping
- Imtakt silica ODS: (wide pH range) polyfunctional ODS + polymeric endcapping

http://www.imtaktusa.com/site_media/fil ... TI118E.pdf

Hi mohan_2008

I'm curious about your application - "Injecting pharmaceutical suspension"

I take this as a formulation of small, insoluble particles of api.
So, don't you first have to dissolve this suspension in a solvent
that will dissolve these "insoluble particles?"

Hi Bryan,

At certain low analyte concentrations, we have no choice except to inject the suspension "as is". Several reasons - very low peak count "as is" being the prime consideration. There might be some options wherein we can inject a diluted suspension, but we prefer to inject it straight.

The Vehicle suspensions in our case are just like solutions - except they are thick, gluey and viscous. One excipient is SLS.

Initially, we used to inject them straight as per a method, however pressure starts building up on the column and hence, we started to deviate from the practice.

But, still I am looking for ways if we can do it straight.

Mohan - could you dilute in water and inject a proportionally larger volume to get to the same amount injected?

Hi Uwe,

sorry for not responding promptly. We have a sudden load of multiple projects at work and hence the delay.

I can get around this only for a few methods (but not all the time, when we were only given a choice to change the column), since the suspension is directly shot onto the hplc as per most of our client methods. The client thinks that a dilution is not needed, since our concentration is already at the low level.

Hence, I was looking at an appropriate column that can tolerate a highly viscous suspension injection (I will filter the suspension prior to injection using a 0.45uM PTFE to dislodge any particulates).