(a) What type of ion chromatography (cation or anion) will you use to separate
the following ions: Cu2+, Fe3+, Ag+ and Na+
.
I'm having trouble here as I know that in elution chromatography they use like charges to separate ions, but is that the same case in ion-exchange?
(b) Give the order of elution when the ions are stripped off the column with an
acidic solution. Explain your answer. (3 marks)
(a) To determine the type of ion chromatography (cation or anion) to separate the ions Cu2+, Fe3+, Ag+, and Na+, we need to consider their charges. In ion chromatography, ions are separated based on their charge and charge interactions with the stationary phase.
Cation exchange chromatography is used to separate positively charged ions (cations) based on their charges and interactions with negatively charged stationary phase. Anion exchange chromatography, on the other hand, is used to separate negatively charged ions (anions) based on their charges and interactions with positively charged stationary phase.
In this case, Cu2+ and Fe3+ are cations, and Na+ is also a cation. Since they are all positively charged ions, we would use cation exchange chromatography to separate them. Ag+ is also a cation but is not mentioned whether it needs to be separated.
Therefore, for the ions Cu2+, Fe3+, Ag+, and Na+, we would use cation exchange chromatography to separate them.
(b) The order of elution when the ions are stripped off the column with an acidic solution will depend on the strength of the ionic interactions between the ions and the stationary phase. In general, the weaker the ionic interactions, the earlier the elution.
In cation exchange chromatography, an acidic solution is used as the eluent to strip off the cations from the stationary phase. The order of elution would depend on the relative strengths of the ionic interactions of the cations with the stationary phase.
In this case, Cu2+ has a higher charge than Na+, so it will have stronger ionic interactions with the stationary phase, and thus, it will elute later. Fe3+ has a higher charge than Na+ but lower charge than Cu2+, so it will elute between Cu2+ and Na+. Na+ has the lowest charge among the ions, so it will elute first.
Therefore, the order of elution, from first to last, would be Na+, Fe3+, and Cu2+ when the ions are stripped off the column with an acidic solution.