Proper terminology is very important in science. Brand names or trademarks should not be confused with the names of techniques or methods. I sometimes hear and see people misuse the terms "UPLCTM " and/or "UHPLC" so think we need a short post to clarify the correct use of these terms. Here are some basic definitions of the terms plus background.
"LC" or Liquid Chromatography. A general name for any type of chromatography where liquid is used as a the carrier phase and a solid support is used as the media, often packed into a tube.
"LPLC" or Low Pressure Liquid Chromatography. LPLC often includes chromatography
analysis using glass or plastic columns with very large particle support beads run at pressures ranging
from atmospheric (gravity driven) to several hundred psi (~ 30 bars
max, but more commonly just a few bars). Very large particles are required in this application to aid flow through the support, which in some cases is gravity driven, but in others, a small pump is required to push the mobile phase through the column.
"HPLC" or High Performance Liquid Chromatography: *Used to be called High Pressure Liquid Chromatography to differentiate it from the previous term "LPLC". Now we refer to it as "high performance" chromatography, though both terms are technically correct. Compared to the very large media used in LPLC (mm), HPLC uses micron sized support particles packed under very high pressures in stainless steel (note: sometimes strong rigid plastic columns are used for biocompatible applications) columns to enhance the resolution obtained by many orders of magnitude. As such, the more popular definition changed from "High Pressure" to "High Performance" Liquid Chromatography to emphasize this improvement, but once again the technique itself did not change (marketing). Today, we still refer to all modes of high pressure liquid chromatography separation techniques as "HPLC" or sometimes just "LC". The most commonly used HPLC pumps are rated between 400 and 600 bars maximum pressure (with some capable of 1,200+ bars) though in normal use, we rarely run methods which use pressures over 300 bars.
"UHPLC" or Ultra-High Pressure Liquid Chromatography (or Ultra High Performance Liquid Chromatography) has become both a new marketing term and perhaps a subcategory of HPLC (other subcategory examples include: nano-HPLC, narrow-bore HPLC, and mini-bore HPLC). UHPLC is presently defined as the use of sub-2 μm particles with a low dispersion HPLC system, optionally with a pump capable of > 600 bars pressure. UHPLC is still HPLC. Nothing changed except it implies you will use sub 2-micron particles in the column (in other words, just the particle size is highlighted). Many methods which use sub-2 μm particle columns can and are run on a low-dispersion HPLC systems at pressures which do not exceed 400 or 600 bars [For more information, please read: "Pressure Drop Across an HPLC / UHPLC Column"]. The technique used in all cases is still correctly called HPLC and should be described as such in papers, articles etc.
- For example: We have been using narrow bore columns (2.1 mm ID) containing small particle supports for more than 30 years and never changed the name of the technique used each time we changed the column support type used (e.g. 20u, 10u, 5u, 3.5u, 2,5u, 2.2u...). As a matter of fact, in the late 1980's and early 1990's there was a bug push to use 1.0, 2.1 and 3.5 mm ID columns with 3.5u and smaller particles on low dispersion systems to both save solvent, increase performance and reduce run times. This required the use of HPLC systems which were optimized with low dispersion flow paths such as the Hewlett-Packard model 1090 HPLC system (DR5 pumps). Perhaps the technology and methods came too early? Columns with very small particles proved difficult to pack (poor RSD batch to batch). The solvent savings and reduced run times just did not interest people at that time and after a few years, the lack of interest resulted in few commercial columns being available with these properties (I recall packing many of them myself in the lab).
"UPLCTM" or Ultra-Performance Liquid Chromatography is a Trademark of the Waters Corporation. Waters Corporation uses it as a marketing term for their own product technology. Defined by Waters as, "the use of sub-2 μm particle columns in combination with low dispersion, high pressure (15,000 psi or 1,034 bar) instrumentation". The confusion seems to come from: (1) New users of HPLC who think that the name "UPLC" is the name of the technique OR (2) HPLC user unfamiliar with other brands of instruments, using the Water's trademark of "UPLC" to describe the technique of HPLC or an HPLCinstrument with a pump which is capable of exceeding 600 bars pressure OR having a low dispersion flow path. They should be using the term HPLC in all of these cases or optionally, UHPLC, another general marketing term, not "UPLC" (unless they really are referring to a Waters product name or specifically, technology).
Summary: In general, as long as the back pressure is above ~30 bars and/or you are using packed LC columns with particles less than ~ 50 microns in diameter (newer, monolithic supports and superficially porous particles also qualify), then the technique used is always called HPLC. If you are using sub-2μm particles and the system operating pressures for the method are at or above 600 bars, then the term "UHPLC" could be used as well (not UPLC® unless you are specifically using a Waters Corp "UPLC" branded system under the same conditions described), but the term HPLC is far more accurate. You are always correct describing the techniques used as HPLC and we encourage you do so in all articles, papers and discussions.Key take away ... Changing the particle size of the support used AND/OR operating with system back-pressures above 600 bars does not change the name of the technique used (It is still "HPLC"). Please do not confuse marketing names (created in the hope of selling more systems) with the actual name of the analytical technique.
Thanks for explaining this. Sounds like vendors made up the name to convince customers that the system they have is no good and they need to buy a more expensive system with a different label on it!
ReplyDeleteI wonder how many high pressure systems (>800 bar) are still running 10-20 minute methods at 'regular hplc' resolutions.
ReplyDeleteYou would think that scientists would know that the 'U' in UHPLC (or UPLC) was just a marketing campaign to convince users that they needed to buy new HPLC systems with higher max pressure ratings? It seems that some were ignorant and swept up in the sales adverts. We should not call it "UHPLC" at all, but HPLC. All high pressure liquid chromatography is HPLC. Running at higher pressures or using smaller particles would have meant that we would have changed the name everytime we reduced particle size or ran at higher pressures (which we did not do because the name HPLC took care of it). UHPLC is not novel or unique at all. It is still high performance liquid chromatography. HPLC by definition has NEVER specified a specific pressure or particle size. Once we went from "LC" to "HPLC", that name change took care of ALL changes needed. All methods which run at any pressure substantially above gravity flow system (as used in "LC" systems) with packed columns are HPLC methods, not UHPLC or UPLC methods.
ReplyDelete'HPLC Expert' is correct. Let's stop making up new names for a technique that already has one. To do otherwise makes us scientists look ignorant.