the pH of the column was equal to the pH of the distilled water Once the pH of

The ph of the column was equal to the ph of the

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the pH of the column was equal to the pH of the distilled water. Once the pH of the column was equal to the pH of the distilled water, the washings and the eluate was then titrated with the standardized 0.100 M NaOH solution with phenolph- thalein indicator to determine the amount of H + displaced. The titration was done in triplicate. RESULTS AND DISCUSSION How does Ion-Exchange Chromatog- raphy Work? Ion-exchange chromatography is an analytical process where ions held on to the surface of a resin are ex- changed for ions in a solution that is in contact with the said resin. (Skoog, et. al., 2004). The ion-exchange resin will contain a reference ion (H + for cation-ex- change and OH - for anion exchange resins) which will pre-dominate in the resin (the amount of this refer- ence ion bound to the resin is know- able) and in the solution (the pH of the solution in which the resin is im- mersed is also knowable since it can be calculated when the column is be- ing prepared). Since the concentra- tion of the reference ion in the resin and in solution is known and con- stant, the amount of reference ion that will be displaced (the amount of this reference ion in the solution will increase), will be used to calculate the amount of cations that is present in the analyte solution. (Skoog, et. al., 2004). Factors Affecting Ion-exchange Since ion-exchange chromatography relies on the attraction of the ions in a solution to the resin, ionic poten- tial, is very important, because it de- termines the strength of the electro- static bond between H + and the resin. In other words, it determines an ion’s affinity to the resin. (MIT Open Courseware, 2011). Ionic Potential = IonicCharge Atomic Radius Equation 2: Ionic Potential is the ra- tio between the Ionic Charge and the Atomic Radius Since the trend for the increasing atomic radius and decreasing ionic charge is through left of the periodic table, going downwards, it can be deduced, that Group I and II metals will have less elution time and affin- ity to the resin. (Petrucci, et. al., 2011). Another trend is the number of cross-linkages between the resin’s molecules. The resin used, Dowex 50 cation exchange resin, is a ground polymer consisting of phenyl, alkyl, and sulfonyl groups. The sulfonyl group (SO 3 H), acts as the ligand that will produce the acidic Hydrogens that will be displaced by the Copper (II). The sulfonyl groups also acts as the binding site for the Copper (II) and other cations that may be present in the solution. (Skoog, et. al., 2004).
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Figure 1: Structure of the Dowex 50 Cation Exchange Resin shows that the resin contains numerous cross linkages (Blaber and Harvey, n.d.) It can be shown from Figure 1 that the resin contains numerous cross linkages which reduce the number of binding sites for Copper (II) and thus produce a slower rate of reac- tion. This has no adverse effect, since the number of cross linkages does not reduce the amount of Cop- per (II) binding to the resin, but it only slows down the reaction. But, it must be taken into factor that it will definitely slow down the reaction be-
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