Chromatography Forum

Hi. I was reading on wikipedia that HPLC refers to column chromatography where a pump is used to apply pressure to the column and make the process faster. Okay, so I have a couple of questions about this.

1) Is this pressure the same as "back pressure"? Because when I read about monolithic columns, its said that monoliths experience lower back pressures. But at the same time there are HPLC monoliths. What exactly does this mean?
2) So what exactly defines an HPLC column? Are all monolithic columns by definition HPLC?

Any feedback is greatly appreciated.

Alan

"HPLC" is not an officially-defined term, so what "defines" an HPLC column is that someone chooses to call it an HPLC column. A bit of Humpty-Dumpty logic there *.

The official term is "Liquid Chromatography" ("LC"). Variants are used to differentiate specific subsets, often more on the basis of marketing than any fundamental difference. Examples include:
HPLC = "High Performance Liquid Chromatography" or "High Pressure Liquid Chromatography"
FPLC = "Fast Protein Liquid Chromatography"
IC = "Ion Chromatography"
UPLC = "Ultra Performance Liquid Chromatography" (that one is trademarked)
UHPLC = "Ultra-High Perormance Liquid Chromatography"
SDPLC = "Super-Duper Performance Liquid Chromatography" (okay, I made that one up just to see if you were paying attention )

The "HPLC" acronym entered the lexicon in the late 60s / early 70s to distinguish the then-new technology of using columns packed with very small particles to minimize peak broadening during the separation. The catch was that such columns have a high flow resistance and so cannot be used with simple gravity or vacuum-assisted flow.

Today, the term is generally used to describe any "instrumental" version of liquid chromatography utilizing a pressurized system to maintain constant flow and usually a flow-through detector. The monoliths have a lower flow resistance than equivalent packed columns, but the flow resistance is still far too high to operate via gravity and/or vacuum, so most people would include them under the "HPLC" category.



* "When I use a word," Humpty Dumpty said in rather a scornful tone, "it means just what I choose it to mean -- neither more nor less."
"The question is," said Alice, "whether you can make words mean so many different things."
"The question is," said Humpty Dumpty, "which is to be master - - that's all."
Through the Looking Glass; Lewis Carroll

ok thanks for the response, because i was getting a little confused looking at the Dionex product catalog. They have a selection of monolithic columns for various molecular seperations (nucleotides, proteins, etc.) and only some of them are explicitly referred to as HPLC in their description. Should I assume that these columns are compatible with HPLC instrumentation as well?

And while we're on topic, I just want to clarify exactly what is meant by back pressure. Is it the pressure inside the column due to flow resistance? And in the product catalogs for columns, they all have a specific operating pressure (range). Is this referring to the pressure inside the column during operation?

P.S, he kind of thing that I'm looking at right now is this:http://www.dionex.com/en-us/products/co ... 73380.html

Generally speaking, if the column is stainless steel, then it is mostly compatible with HPLC instrumentation (there are some vendor-to-vendor differences in end fittings). If the column is glass, then it is probably not compatible with HPLC without using some type of adapter.

And while we're on topic, I just want to clarify exactly what is meant by back pressure. Is it the pressure inside the column due to flow resistance?

Yes

...they all have a specific operating pressure (range). Is this referring to the pressure inside the column during operation?

Specifically, the pressure drop (difference in pressure) between the column inlet and outlet during operation.

ok sweet. Thank you, this was very helpful.