The figure on the next page shows the overlaid spectra of phenacetin, aspirin, a
ID: 1030849 • Letter: T
Question
The figure on the next page shows the overlaid spectra of phenacetin, aspirin, and caffeine. The spectra are shown from 225nm-300nm. Note that 3 wavelengths have been selected and marked. The compounds were prepared in 90% water:10%methanol with 0.05M ammonium formate at pH 4.8 as the modifier.
1. If the 0.05M NH4OAf was replaced with 1% H3PO4, would you expect the spectra to change and why do you expect that? (more than a Yes or No answer.)
2. If you were to choose one of the three marked wavelengths as the one to use to monitor the chromatographic separation of these three compounds, which one would you choose? (Your decision should be based on the consequences of wavelength error, the consequences of absorbance error, the relative concentrations of the components you are separating, and the relative absorptivities at each wavelength (essentially the component sensitivity. present clear arguments for it.)
0.2A= 26.8mm Asp A- 166.8mm Caf A 69, 8 min Phe A9.0mm Aspirin 0.147 gdm 0.2A Caffeine 0.0315gdm Phengcetin 0.00948 gcm i 250 300 nmExplanation / Answer
pH of the medium can affect the absorbanc values if the compounds under examintion has functional groups with exchangeable protons such as hydroxy, amino , carboxyl groups etc., if ammonium formate is replaced with phosphoric acid , then the spectra will defenitely change in the case of phenacetin and aspirin as they have exchangeable protons , caffeine doesn't change since it doesn't have -OH or -NH2 groups