Capacity and Charge Density
Posted: Sun Sep 28, 2008 10:28 pm
Hans,
The diameter I was referring to is the diameter of the coating particle, assuming the substrate particle (the inner core) diameter is unchanged.
Of course, changes to the aggregate diameter could be so large that they are larger than the column ID but what I was referring to is coating particles that are in the range of 1% of the substrate particle diameter. In this case, modest changes in the coating particle diameter will change capacity but not selectivity or efficiency.
Re: "Also, I have considerable problems with the apparent dichotomy between the number of ionic sites in a colunmn and capacity in IC. For instance: It seems to me that if the equilibrium of an analyte ion lies completely on the side of the stat phase the capacity equals the number of ion sites." I'm not sure what dichotomy you refer to. The capacity of the column (at least the breakthrough or static capacity) is the same as the number of ion exchange sites, at least when both are expressed in terms of equivalents per volume. The distinction JA and I were discussing was that capacity can be added "homogeneously", in which case the concentration of ion exchange sites will change as the capacity changes or “heterogeneouslyâ€
The diameter I was referring to is the diameter of the coating particle, assuming the substrate particle (the inner core) diameter is unchanged.
Of course, changes to the aggregate diameter could be so large that they are larger than the column ID but what I was referring to is coating particles that are in the range of 1% of the substrate particle diameter. In this case, modest changes in the coating particle diameter will change capacity but not selectivity or efficiency.
Re: "Also, I have considerable problems with the apparent dichotomy between the number of ionic sites in a colunmn and capacity in IC. For instance: It seems to me that if the equilibrium of an analyte ion lies completely on the side of the stat phase the capacity equals the number of ion sites." I'm not sure what dichotomy you refer to. The capacity of the column (at least the breakthrough or static capacity) is the same as the number of ion exchange sites, at least when both are expressed in terms of equivalents per volume. The distinction JA and I were discussing was that capacity can be added "homogeneously", in which case the concentration of ion exchange sites will change as the capacity changes or “heterogeneouslyâ€