I've seen a bar plot on the Waters web site comparing a number a phases with Symmetry Shield.

Why is there a difference in tailing factor for the base probe and why do the last two peaks in the chromatogram change elution order ?

Thanks

I've seen a copy of this plot.

Basically, Waters are being sneaky and comparing a polar embedded phase with mainly alkyl chain chemistries. Really this is like comparing apples with pears.

The polar embedded phase will give better peak shape for the basic marker, but then again, so would any other polar embedded phase (eg. HyPurity Advance).

The change in peak elution order seen in the chromatograms is typical of a polar embedded phase. There are many other compounds, for example nicotinic acids, which will change elution order between C18 and polar embedded phases.

My final comment is that Waters must believe that we are blind not to notice the glaring errors in their work. It would not suprise me if some of the other manufacturer's mentioned didn't publish a reply - after all mud sticks.

The reality here is if you say "polar embedded phase" to most people doing chromatography they look at you like you are talking a different language. All most want to know is "will this column stop tailing peaks with my basic compounds?". This of course assumes that they have any idea what a basic compound is. I personally did not see the glaring errors (I must be blind) all I saw was one column showing better performance under test conditions. BTY, most other column makers publish similar documents(surprise, surprise) showing thier products better than others under test conditions.
Its not sneaky, its marketing.

Enough said.

I would be interested to hear about the "glaring errors" in my work...
Phases with an embedded polar group give improved peakshapes especially for basic analytes. They also result in different selectivities, especially for analytes with polar functionalities. At the same time, the retention is comparable to the retention of classical C8 or C18 columns, which is not the case for CN columns.
One needs to differentiate though between two different groups of packings with an incorporated polar group. One group is synthesized in a single step on the surface. This guarantees a high reproducibility of the packing. SymmetryShield is an example of this. The other group is synthesized in a multi-step process. This is especially true for some of the older phases of this type, but unfortunately also for some of the newer phases. Especially the amide type is often created in a two step process, which leaves amine functions on the surface. These amine functions result in excessive retention and tailing of acids. Thus a chromatographic test with acids as samples can easily discriminate between phases that have been created in a single step process and phases created by a multi-step process.

Uwe Neue