Chromatography Forum

This is practice question during lecture (not HW). I didn't hear the professor clearly. Can you help me with this question? In fact, I'd add the question "Why the answer is normal-phased HPLC?

Which technique is more susceptible to column overloading, reversed phase HPLC (C18 stationary phase) or normal phase HPLC?

In fact, unless there are other qualifications to the question (e.g. did the instructor specify a particular normal-phase column), the answer is *not* normal-phase chromatography. You might want to talk to the prof and ask for more detail.

I'm getting a bit pedantic here, but the distinction between normal-phase and reversed-phase chromatography is fundamentally the relative polarity of the stationary vs. the mobile phases. There is nothing in that definition that makes one inherently lower capacity than another.

A more useful comparison might be between liquid-liquid partition chromatography and liquid-solid adsorption chromatography. Reversed-phase separations on many C18 columns can be explained as partition between the bulk mobile phase and a solvated layer on the surface of the stationary phase. That tends to lead to a high phase ratio (i.e., that nice thick solvated layer represents a lot of stationary phase and therefore high loadability. Normal-phase separations on bare silica or alumina are more easily explained as adsorption of analytes onto the polar surface. Because the stationary phase is a surface instead of a layer of liquid on that surface, there is less of it, and therefore limited loadability.

The catch is that many (if not most) normal-phase separations today are carried out on polar bonded phase columns instead of bare silica and are arguably based on partition into a solvated boundary layer rather than on adsorption.

Note that all of the above are gross oversimplifications of complex phenomena!

In fact, unless there are other qualifications to the question (e.g. did the instructor specify a particular normal-phase column), the answer is *not* normal-phase chromatography. You might want to talk to the prof and ask for more detail.

Well, he usually shows some questions and answers himself right after the lecture on the topic and this was one of those questions. What I am realizing now is that some of these questions, though written in short and concise form, requires explanation in a long way as a way to re-inforce the lecture, rather than testing to see how much the student got out of the lecture. I say that because I didn't remember his explaining the way you explained below using phrases like "liquid-liquid partition Chromatography" and "liquid-solid adsorption Chromatography" which totally cleared it up for me.

I'm getting a bit pedantic here, but the distinction between normal-phase and reversed-phase chromatography is fundamentally the relative polarity of the stationary vs. the mobile phases. There is nothing in that definition that makes one inherently lower capacity than another.

A more useful comparison might be between liquid-liquid partition chromatography and liquid-solid adsorption chromatography. Reversed-phase separations on many C18 columns can be explained as partition between the bulk mobile phase and a solvated layer on the surface of the stationary phase. That tends to lead to a high phase ratio (i.e., that nice thick solvated layer represents a lot of stationary phase and therefore high loadability. Normal-phase separations on bare silica or alumina are more easily explained as adsorption of analytes onto the polar surface. Because the stationary phase is a surface instead of a layer of liquid on that surface, there is less of it, and therefore limited loadability.

The catch is that many (if not most) normal-phase separations today are carried out on polar bonded phase columns instead of bare silica and are arguably based on partition into a solvated boundary layer rather than on adsorption.

Thanks for the explanation including how normal-phase separations today are carried out.

Note that all of the above are gross oversimplifications of complex phenomena!

I hear you:)

I am looking for the early history of Chromatography information. I have term paper to finish before Feb 9, 11. I have to include the inventors or contributors, Tswett, Martin and Synge in my papers. I have been looking through internet and collecting some useful information. But I couldn't find significant for those who discovered about Chromatography. If anyone have any useful information like links, I'd appreciate it. Thanks in advance. My textbook " Creation Of Fire by Harlod Goldwhite, Cathy Cabb" doesn't have any particular mentioned about Chromatography. Thank you in advance

I hate to say it, but if you look for some of the names you suggest in Wikipedia, you will get quite reasonable articles. Of course copying wikipedia is a classic way of failing term papers as your examiner/tutor is probably well aware of wikipedia's content, but wikipedia does provide some links to other, more original sources, and you can follow them. For Tsvet, it really helps if you can understand some German though!

Hi

For Martin and Synge there is also some information at the nobel prize organisation homepage (http://nobelprize.org/nobel_prizes/chem ... ates/1952/#), their biographies are included.

(From Nobel Lectures, Chemistry 1942-1962, Elsevier Publishing Company, Amsterdam, 1964

This autobiography/biography was written at the time of the award and first published in the book series Les Prix Nobel. It was later edited and republished in Nobel Lectures. To cite this document, always state the source as shown above.)

Thank you guys so much. Unfortunately, my teacher don't want us to make a reference from wikipedia and he prefers us to use ACS journals or some chemistry journals. Thank both of you for your time.

Showing my biases here, try McWilliam or Dewar or Randall Hall or, especially, Lovelock. You will find some of the pioneers. Lovelock has a delightful article on his personal journey in one of the major journals (on my wall at work as inspiration.)

Best regards,

AICMM