Amino vs. Cation exchange columns - Stability, Durability

[lqd]

Hi all,

From your experience, what about stability, reproducibility, durability, etc. of cation exchange columns (e.g. Ca, Pb, Ag) for carbohydrate analysis in honey?

Till now I have used only amino columns from various brands but now I ‘m thinking of buying a cation column with its own guard column, but I have heard, apart from their better separation generally, that they last even for a shorter period of time and that they deteriorate faster than amino columns.

Is that true? Any advice would be really appreciated.

[Gerhard Kratz]

Due to the surface chemistry NH2 columns are more difficult to produce lot to lot the same and life time is short in general. Cation exchange columns are more difficult to handle. Ca+ you need to rinse minimum over night before the first use and keep always enogh mobile phase when you run the column with low flow over the weekend. Column temperature is usually 80°C and without mobile phase packing material will be destroyed. But if you handle your cation echange column with care column lifetime is longer than ythe Amino columns.
Good luck.

[lqd]

Many thanks for the info..so if i understand it right ion exchange columns need continuous wetting with the mobile phase (usually water) at high temperatures overnight,weekends,etc regardless the manufacturer. Or are there available on the market any ion exchange columns without so specific and strict needs?Any suggestions for specific models which have been tested in "real life" (lab) and worth to be suggested?

[tom jupille]

The cation exchange columns used for carbohydrate analysis are almost all highly sulfonated PS-DVB (polystyrene-divinylbenzene copolymers). The selectivity will vary depending on the counterion (H+, Ca++, Pb++, Ag+ are the most common). The packings are "semi-rigid", which means that the beads can shrink/swell depending on the ionic strength of the mobile phase and on the counterion (that's why you can't convert from one form to another in situ). The retention mechanism is unique to these columns (and different from that on amino bonded phase columns or anion exchangers at high pH).

They are actually quite robust -- considerably longer-lived that most silica-based amino bonded phase columns. You run them and store them in deionized water, period. You *do* have to watch out not to over-pressure the columns (the beads are plastic and will deform and pack down) and don't put methanol in the mobile phase, but aside from that they are pretty much bullet-proof.

The high operating temperature has nothing to do with column storage, but comes from the fact that the columns will partially separate the alpha- and beta- anomers. Since mutarotation is actually fairly slow at room temperature you tend to get broad peaks as the two forms interconvert. Running at elevated temperature speeds up mutarotation so that you see single, sharp peaks representing the "average" of the two forms.