Hi again, Parkc23,
I didn't realize that you weren't a chemist...but that's okay. We all start off as something else....
HPLCaddict is quite right to emphasize what I said in more detail...please let me ask, What kind of LC instrumentation do you have or are trying to learn about? In practice, using the SPP columns is much the same as using completely-porous particles of < 2 um in diameter...the goal is to have As Little Volume in the LC system as possible. My experience with SPP columns mirrors HPLCaddicts...they will be most efficient on a UHPLC (such as those I named below) due to low their low system volumes as compared to HPLC equipment designed best to use larger-bore columns containing larger particles.
One old selling point on SPP stationary phases also was---these don't generate As High Backpressures as the < 2um completely porous materials...this is true for comparably-sized particles of both classes overall (2.7 um core + 0.5 um porous silica generates backpressures Generally Less than say 3 um completely porous material) when the Same Column Diameters and Lengths containing these particles are compared.
I'll finish later. Children...are interesting, I love them, but at times...
If you are willing to optimize your HPLC system or directly use these SPP columns on a UHPLC they can give results comparable to sub-2-micron materials concerning efficiency. As HPLCaddict continues...
"Nevertheless
- be warned that SPP columns will still generate relatively high pressures. I've made the experience that a lot of analysts have no problems running a UHPLC at 950 bars ("because it was made for high pressure") but for routine work on a HPLC they start to grump at pressures higher than ~250 bars.
- SPP columns tend to give less retention than fully porous particles because of lower surface area. You might have to adjust your methods accordingly.
- make sure that your detector is fast enough to catch all those nice slender peaks.
- don't forget that chromatography is not all about efficiency. Selectivity should be the first concern!!"
Agreed on all counts...already talked about backpressure a bit. SPP is not a "cure" for backpressure...a UHPLC is "better" with SPP and smaller completely porous columns for TWO reasons...their ability to handle Higher Backpressures and Smaller System Volumes to start with out of the crates, so-to-speak. You'll not be able to inject as much mass and/or volume onto SPP as completely porous materials...for the physical (not as much stationary phase to contain solutes) reason. Need a fast data acquisition rate to capture peaks that completely elute in one second or much less, at times, yes. Last statement...well, that one goes almost without saying for any type of stationary phase in (U)HPLC.
As to the idea that larger column ID is "Better" than smaller ID for efficiency (narrower peaks), not necessarily so. A solution injected onto a column generally travels first through capillary tubing, then through the column, then more capillary tubing, a detector of some sort and out to waste or another detector or more, a fraction collector...whatever. In any case, the injected solution volume will have an opportunity to expand as it travels through all of this capillary tubing, the column and the detector(s) due to these phenomena called "laminar flow" as well as ordinary good old "entropy." All of this expansion of the injected solution has Nothing At All to Do with the stationary phase's efficiency, but this expansion makes the Apparent Efficiency of the stationary phase "Seem" less than it ought. If 4.6 mm ID OR a 2.1 mm ID column were filled with the same type of material, like vs. like, say, SSP material of one type, given the same isocratic conditions for both columns and the plumbing of the LC remaining constant, the measured efficiencies of peaks, particularly the early eluting ones, generated on the 2.1 mm ID column Will Be Greater in plate count than those made using the same analyte(s) on the 4.6 mm ID column--also providing, of course, that the injected volume is the same for both and is of a reasonable size for the narrower column (not as much space in the 2.1 mm ID to "put stuff." Alternatively, if the tubing is wide and/or the detector cell is large...all the smallness of the 2.1 mm ID column would be defeated...there would be too much room for the injected solutes to expand in space in every location except the column...and in the case of the 4.6 mm ID column, not as much apparent "Damage" would be caused to the peak widths and heights of the injected solutes as they would have lots of room to expand in the column as well. In this way, a 2.1 mm ID column can appear to be "less efficient" than a 4.6 mm ID column when both have the "same-sized" stationary phase within them.
HippyLabRat--a mistake I still make occasionally is in regarding the distinction of "resolution" and "efficiency". It's possible to have "poor" resolution (distance between adjacent peaks at their base) where the selectivity (alpha, or put another way, distance between the peak apexes) is > than 1. In this case, the peak are wide, the efficiency of the peaks are poor...it's also possible to have "poor" resolution when the peaks' efficiencies are excellent (narrow) but the selectivity of the peaks is poor (alpha < 1).
In the first case, narrower capillary tubing, narrower column ID, smaller detector cell volume and other factors I'll not list in detail can help the efficiency of the column "come through" by not allowing the efficiency of the stationary phase be lost due to volume expansion.
It's important to "marry up" the column ID with the (U)HPLC system dead volume.
I Love Mac-Mod...
http://www.mac-mod.com/resources-reports.php
The "Guide to Ultra-Fast HPLC" really says it all. The other references are also great background, and explain things a bit differently than I do. Almost forgot...practical stuff...even if you choose to use 4.6 mm ID columns, the best performance will be afforded with a LC that has as low a system volume as possible...though older analytical scale LCs will "work"...just not as well as more optimized systems for low volume.
. They spoke quite frankly about this topic and even admitted that recently introduced 1.3µm SPP particles are quite senseless at the moment, as even decent UHPLCs have too much dead volume to really use these.
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