I\'ve come up with answers but I need some clarification. Would the answer to a)
ID: 1062285 • Letter: I
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I've come up with answers but I need some clarification. Would the answer to a) be the 3rd ionized form? Would there only be hydrophobic interactions for b) And does the first ionized form have the shortest retention time and third having the longest? No SIMM 11:21 AM Problem Sets Question 2 (12 marks) Tyrosine is a triprotic amino acid with pKa of2.17, 9.19. and 10.47The first proton is removed from the carboxylic acid (-COOH), the second from the protonated amine group NHs ).The third, with a pKa of 10.47. is the phenolic proton (-OH) on the aromatic ring. At low pH, the molecule is a monocation. At high pH values, it is a dianion. (Recall: you did this on Problem Set 2) Tyrosine The capacity factor of tyrosine changes with pH on a reverse-phase support. With a phosphate buffer of 0.02 M and solvent comprised of 5:95 (vlv)ethanolwater, the pH values and the associated k values were determined to be: pH 15 4.59 2.70 2.88 1.90 4.40 5.80 1.86 1.80 7.22 8.83 0.88 a) If the mechanism of retention is strictly a reversed phase one, which form of the molecule would have the highest k ?Briefly explain (max. 50 words) b) What type(s) of interaction(s) is/are occurring on this reversed phase column between stationary phase and analyte? eg. H-bonding (adsorption), reversed-phase, hydrophobic ion exchange, exclusion...? c) If each of the ionized forms of tyrosine was analyzed separately using the same stationary reverse-phase and solvent, arrange these tyrosine forms in the order of increasing retention times (ie from the shortest retention time to the longest). Page 2 of 5 20%Explanation / Answer
In a reverse phase column the stationary phase is non-polar in nature. With 5 : 95 = ethanol : water mobile phase, water being more polar would elute the most polar component first out of the column.
(a) The k' for first isonization would have highest value as the moelcule obtained after first ionization is neutral -COO- and NH3+ in the structure.
(b) The type of interaction here working is hydrophobic ion interaction.
(c) The retention time for first ionization would be shortest as we form a neutral species after first ionization which can form hydrogen bond with water solvent and gets eluted first. The retention time for the third ionization would be longest as it intercacts the stringest with stationary phase.
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