By Anonymous on Wednesday, June 30, 2004 - 07:16 am:

Does anyone knows how to determine the residual Chlorothalonil (a fungicide) using an HPLC with a Hypercarb column?I have problem because this column consists of pure graphite and the interactions between the analytes and stationary phase are different compared to the common columns with C8 and C18. Does anyone has an idea?Thank you all

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By Constantin Sychov on Wednesday, June 30, 2004 - 08:06 am:

The retention on PGC is driven mostly by two mechanisms: one is "charge-transfer" and another is "reversed-phase". Contribution of each of the mechanisms depends upon stucture of an analyte and polarity of the mobile phase. In highly polar aqueous mobile phases, in case of polar analytes, PGC works as reversed phase of very high hydrophobicity. If a mobile phase is more non-polar, and analytes are composed of non-polar pi-fragments (aromatic rings, ...), pi-interactions (charge transfer uinteractions of pi-pi type) tend to reveal theirselves more intensively. In totally non-polar environments PGC retaines aromatic and other pi-containg analytes due to pi-interactions. The eluotropic raw of solvents for this mode (it was called quasi-normal-phase HPLC) is the following: hexane < isopropanol << ethylacetate, THF < toluene < acetone < chloroform, CH2Cl2 (in order of increasing of elution strength, data for naphthalene on hypercrosslinked polystyrene).
I dont know the structure of your analyle, and cant offer particular composition of mobile phase. But you can contact me by e-mail.

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By Anonymous on Thursday, July 1, 2004 - 12:52 pm:

Why do you want to use a Hypercarb column for chlorothalonil? Chlorothalonil would take a very long time to come off of a graphite column. Using a cyano or phenyl column would probably be a better choice.

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By Constantin Sychov on Friday, July 2, 2004 - 02:25 am:

There`s one case when PGC can be better than conventional reversed phases, - when used with on-line SPE on new polymeric and even graphitic sorbents.

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By Jimmy on Tuesday, August 10, 2004 - 06:46 pm:

Constantin,

Why is PGC better with online SPE? Because it is more retentive and more compatible with highly aq. washing solvent for the SPE?

Thanks!