Anal Chim Acta. 2017 May 15;967:12-32. doi: 10.1016/j.aca.2017.01.060. Epub 2017 Feb 7.
Recent advances in stationary phases and understanding of retention in hydrophilic interaction chromatography. A review.
Jandera P1, Janás P2.
I was looking for efficiency of gaurd column on its own for various compounds and for linking up of gaurd columns.
The fact is that e.g. phenyl column coupled to C18 column improved resolution (related to void volume in capacity factor) defied my understanding of mixed mode chromatography.
The journal: J Chromatogr B Analyt Technol Biomed Life Sci. 2013 Dec 15;941:116-22. doi: 10.1016/j.jchromb.2013.10.005. Epub 2013 Oct 16.
Liquid chromatographic mass spectrometric method for simultaneous determination of smallorganic acids potentially contributing to acidosis in severe malaria.
Sriboonvorakul N1, Leepipatpiboon N, Dondorp AM, Pouplin T, White NJ, Tarning J, Lindegardh N.
serially links ZIC HILIC Gaurd column to ZIC HILIC which is common research for polar analytes.
Mel, The peak resolution is dependent on three variables. See Purnell's equation.
1. Selectivity function of stationary phase chemistry, mobile phase, temperature
2. Column efficiency (number of plates)
3. Retention factor k
If any variable changes, you will get a different value of resolution. It is not surprising that one can play with resolution by coupling columns of different chemistry or in other words selectivity. The main problem is that it is difficult to predict what is going to happen if we couple columns of different chemistries because we do not know what is going to happen to selectivity.
The guard column is nothing but a short column. We do lot of separations on guard columns 0.5 to 2 cm long, which we make ourselves, for very high speed separations. But consider that type of work as a very special case (of academic research). There are lot of challenges with using a guard column for separations and not many people do this work.
For the other part of your question on the effect of serial coupling on plate counts: Let us assume you have a 10 cm long packed column of your desired chemistry. Now if we have twenty 0.5 cm long columns (or say guard columns) connected in series with the same particles, you will get the same separation, same efficiency, and same resolution, at least in theory. In practice, each short column connection is going to degrade the analyte band travelling in the columns. The serially connected column would most likely show poorer performance than a single 10 cm long column.
Mel, The peak resolution is dependent on three variables. See Purnell's equation.
1. Selectivity function of stationary phase chemistry, mobile phase, temperature
2. Column efficiency (number of plates)
3. Retention factor k
If any variable changes, you will get a different value of resolution. It is not surprising that one can play with resolution by coupling columns of different chemistry or in other words selectivity. The main problem is that it is difficult to predict what is going to happen if we couple columns of different chemistries because we do not know what is going to happen to selectivity.
The guard column is nothing but a short column. We do lot of separations on guard columns 0.5 to 2 cm long, which we make ourselves, for very high speed separations. But consider that type of work as a very special case (of academic research). There are lot of challenges with using a guard column for separations and not many people do this work.
For the other part of your question on the effect of serial coupling on plate counts: Let us assume you have a 10 cm long packed column of your desired chemistry. Now if we have twenty 0.5 cm long columns (or say guard columns) connected in series with the same particles, you will get the same separation, same efficiency, and same resolution, at least in theory. In practice, each short column connection is going to degrade the analyte band travelling in the columns. The serially connected column would most likely show poorer performance than a single 10 cm long column.
I agree with the above answer. Note; separation does not include the flow rate!
We also use guard columns occasionally as analytical columns, especially if the analyte is highly retained on the conventional analytical column. You have the advantage with a guard column (I use the 20 mm ones) of being able to achieve extremely high flow rates (and thus rapid turnaround) with low back pressures. I have tried coupling them before and you get exactly the effect that Farooq predicts; a degradation of the chromatography relative to a conventional column. I also have tried coupling different phases together and was very disappointed with what I got. The biphasic coupling is a lot more complex that what it appears on paper.
Hi Mel, maybe this will be helpful to you:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2939347/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4559102/
https://www.ncbi.nlm.nih.gov/pubmed/26362810
https://core.ac.uk/download/pdf/9396771.pdf
http://pubs.acs.org/doi/abs/10.1021/acs.analchem.5b03615
https://www.researchgate.net/publication/266399202_HILIC-MS_for_metabolomics_An_attractive_and_complementary_approach_to_RPLC-MS
http://pubs.rsc.org/-/content/articlelanding/2016/ay/c5ay02528a/unauth#!divAbstract
Greetings Markus
Article HILIC-MS for metabolomics: an attractive and complementary a...
My personal trick is, use higher flow rate and shorter column for the second dimension
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