Chromatography Forum

Hello

I would to suggest you great HPLC column (not chiral) to improve your C18 column. This one is the Cholester column. I used many times in my lab to get great separation, and avoid to pay lot of money for chiral column

Good Luck
Charles

Charles...

You have not answered my question: why do you think that a cholesterol column would be good for a chiral analysis? And please be careful with your answer...

[quote="Uwe Neue"]Charles...

Uwe

The cholester HPLC columns have chiral center, and most of the time this is the column that I used when I need to improve my reversed phase stationary phase, as C18. I dont say it is working all the time but before to spend lot of money for chiral HPLC columns, I start with this one. This column should be classified by USP this year because many QC lab have lot of succes. But the cholester column has some bleeding in LC-MS, not good for that kind of detector.

Charles, are you talking about a column that has cholesterol attached to the stationary phase via an ester linkage?
I think Uwe is talking about a column (achiral) which has been optimized (or whatever) for cholesterol analysis?

Before I start, let me point out that my company is not selling any chiral phases - just in case that somebody might think that there is a commercial bias in my answer...

In order to achieve chiral separations, people have designed specific stationary phases with specific chiral centers. These chiral centers have different types of binding sites built around the center (Pirkle, for example), or interactions with a multitude of functional groups arranged in a complex structure (Armstrong, for example). While cholesterol is a chiral compound, it does not offer a range of binding sites, just some boring and non-selective hydrophobic sites. THIS is the reason why cholesterol is a VERY poor candidate stationary phase for a chiral separation.

You can get other selectivities from cholesterol, but nobody has proven to me yet any magic that is any different from the selectivity difference between a high-density and a low-density C18.

I just to let you know that I had lot of succes for HPLC chiral separation with cholester column. I am not very good for theory, this is why I believe more in my laboratory assay. Cholester is not magic, but it is works and this is we want to have as analytical chemist. I am doing more than 23 years in HPLC.

I did not say that chiral separations are impossible on a cholesterol column, I just think that it is a very poor choice compared to the myriad of other chiral stationary phases on the market, which all have selective interactions, which cholesterol does not have...

It is just because it better to start with cheaper column. True HPLC chiral column are very expensive and lot of leaching for some of those with semi-prep columns

I feel that screening is usually the best approach, unless you have prior experience. In a previous job we had a column switcher with six columns, and tried 3 methods on all 6 columns. We loooked at the best result from those 18 runs, and optimzed from there. It sounds like a lot of time, and it was, but most enantiomers were separated on a Daicel AD-H or OD-H. IF you decide to go with this approach, I'd suggest a few different types or columns, like some cellulosic/amylosic columns, a pirkle column, a protein column, etc.

However, if you want to try as few columns as possible, you can contact the manufacturers (http://www.chiraltech.com/ and http://www.registech.com/ are a couple) and ask their applications people what they recommend for your structure (if you are allowed to send the structure out). Some of them even have application guides which you can sort by functional group type to find one similar to the one you are working on.

And I found out Regis offers a free screening service (http://www.registech.com/Markets/Chroma ... ening.html) so you may want to check them out if you decide to go the chiral column route. Best,

Chris



Chris Singleton
DMPK
BiogenIdec