Well, THF and dichloromethane are two of the solvents you are not supposed to have there, see the attachment. We have been using a couple of ChiralPak AD-H columns for years without a problem. If extensive IPA washes do not help, it seems to me that the only chance is changing the solvent system to MeOH or MeOH-rich, however this irreversibly will require that this column is used with these solvents only (no going back to hydrocarbon-rich phases).

Rejuvenating can be successful if its a Reverse phase or a silica column.

Generally chiral normal phase columns are so sensitive, it can be maintained properly maximum upto 200 Injection. Peak Broadening may occur when the traces of THF solvent gets coordinated with CSP.  

Hello,

In fact as Jacek Martynow noticed you are not allowed to use these solvents on Chiralpak AD-H. I'm pretty sure that your column is destroyed...if you think that it is solvent issue.

Maybe the problem could also be particules stacking in head of your column (if you are not using a pre-column, if yes change it and try analyses again).

Reverse your colum and flush it 1h with IPA (dont connect the column to the detector but direcltly to the waste)

If you want to use these kind of solvent, I suggest you to use the Chiralpak IA which has the same selectivity than the AD-H but is by far more robust (because chiral selectors are immobilized)

Here is the manual of the column

Kind regards,

Laurent

http://www.mz-at.de/resources/brochures/Chiralpak_IA_Manual.pdf

Laurent,

So, for analytical applications requiring the use of a PDA detector, or a UV detector at wavelengths 250 nm wavelength, or for other types of detection other than UV, the IA version is interesting. My question is, with these limitations is the price of an IA column worth it...

Hello Jacek,

Sure it worth it ! When you replace your old AD-H test the Chiralpak IA which is more versatile for what i noticed.

When i make my chiral screening, I always screen chiralpak IA / IB and IC first.

If i don't have enough resolution (but only a beginning of separation) i'll go next on AD-H and OD-H because selectivity is nearly the same but slightly differ.(sometimes enough to get my 2.0 resolution).

Nevertheless a mix of more exotic solvent (Ethyl acetate, Dichloromethane, MTBE or even 100% acetonitrile) gives sometimes surprising results !

For the loss of sensitivity sure it depends on your compounds functionnalities, your detector base sensitivity as well as your molecule concentration.

Usually i try to adapt the concentration of my sample to have enough sensitivity or i'll find an area in my molecule UV spectrum that suits well with solvent UV cutt-off.

Greetings,

Laurent

Laurent,

Correct, these are old, good approaches... of course with higher concentration many times you lose selectivity for the run, but sometimes it works.

Regards,

Jacek

Thank you very much for your suggestion. i really appreciate that.

Thanks and regard

Unfortunately, you have washed the coated phase off the Chiralpak AD-H column. Please dispose of it and purchase a new one. They can not be cleaned or restored once this happens. Always follow the manufacturer's directions for use of these columns.

The Chiralpak IA column is similar to the AD, but has a covalently bound phase making it resist more abuse. However, this comes with a price that the IA will not resolve anywhere near the number of compounds that the coated phases will. The coated and covalently bound columns will also provide different chromatography too.

William

We need to know more about what really happened there, and about what the condition of the column really is. The columns are not cheap (even the AD-H ones), and replacing them in some cases is a tough call.

After a mishandling, sometimes these columns still can be run successfully using only MeOH as the solvent, which shortens the retention times, but still can work for some applications. The thing is, the nonpolar solvents cannot be used any more after MeOH has been used.

The worst case scenario obviously is as you said, and let's hope that did not happen.

I have used these columns for decades and can assure you that once MeOH has been used on many of the coated phases, the columns are fine. Now, if you used special additives or inappropriate liquids, then you may permanently change the surface chemistry and/or wash some of the phase off the column (altering its selectivity). *All of your chiral columns should be tested with your own std(s) upon receipt (not the pathetic compound used/supplied by the manufacturer for QC). This serves as a benchmark to compare to when you suspect that something may have happened to the column. We use pharma samples which have K1 of greater than 4. I often see columns which have lost most of their coating still pass the manufacturer's QC test, but will not separate any "real" compounds from the past. Having a documented std for each column type really saves time later on when questions arise.

Now, if the user has fouled the column, then a wash with 100% EtOH (or other appropriate solvent which will dissolve the "fouling" material) should be used. If this fails and the selectivity of the column changes, it should be disposed of. If you keep or continue to use a column once it's surface chemistry has been changed, you are now developing methods which can not be easily reproduced. This is what you want to avoid at all cost.

These chiral columns can last a long time and show good reproducible results, but they are delicate and do require some extra care over what most people are used to using, i.e. a typical silica based C18 column.

While the covalently bound versions of these columns are much more rugged, they also do not generate any where near as many good quality chiral methods as the coated phases do. For analytical analysis, I always recommend starting off by screening the coated phases first. Chiral separations can not be done on a single 'universal' column so even though they are expensive, you will need to have several different types of them available for this type of work.

I guess we have been doing these things quite some time. Currently, I am using two AD-H columns and one AD column (500x50 mm).

Yes, what you write is correct and very useful for our community here.

As for the MeOH application, I am attaching a reference that you may find interesting and of use.

Thank you Jacek. I recall reading that paper a few years ago and know many of the authors. I agree with many of the comments about the modifers too.

You may or may not know that in 1992, my company, Chiralizer Services, was the originator of most of the methods, techniques and commercial hardware (inventor's of, The Chiralizer and LC Spiderling Column Selector) used for chiral/achiral HPLC and SFC screening and method development. In the 1980's we developed custom systems for clients to assist them with chiral method development (for analytical and prep HPLC plus GC too). Over the past decades, our company has resolved just under 20,000 drug racemates for just about every pharma company on the planet. Esp for all of those tough samples that the top scientists at those same companies failed at (they do not send us easy samples!), we often found methods in 1 or 2 business days.

We are also very familiar with most of the MD permutations utilizing modifiers, unusual alcohols, additives and screening 'tricks" to resolve chiral racemates apart for both HPLC and SFC. While some of these learned techniques and methods are proprietary to our company, other tips and specialized hardware tools are provide by us to chiral chromatographers.

Our main interest is not to run samples, but rather to help educate and train chromatographers how to resolve chiral racemates apart using the simplest mobile phase, least modifiers and least expensive column. There is a steep learning curve in this specific area and we stress the importance of the fundamentals of chromatography. Most difficulties in this field arise from poor training and understanding. Most practicing chromatographers have little to no training in the field (they are often left to just figure it out themselves). We hope through discussion areas such as this and many others that we can spread practical knowledge, dispel myths and share findings.

BTW: I provide a free "HPLC Hints and Tips" blog page which includes short articles info and on how to improve chiral separations plus much more. Link:  http://hplctips.blogspot.com/

Here is a link to a popular free article on "Chiral HPLC and SFC Column Screening Strategies for Method Development:" ; http://hplctips.blogspot.com/2011/06/chiral-hplc-and-sfc-column-screening.html

Nice!

Thank you.

Jacek