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Consider the following changes that could be applied to the operating parameters for a chromatogram set up to carry out high-performance liquid chromatography (HPLC) with a polar stationary phase and a non-polar mobile phase: I decreasing the viscosity of the mobile phase II using a more tightly packed stationary phase III using a mobile phase that is more polar than the stationary phase Which of the changes would be most likely to reduce the retention time of a sugar in the HPLC? - VCE - SSCE Chemistry - Question 20 - 2020 - Paper 1
Question 20
Consider the following changes that could be applied to the operating parameters for a chromatogram set up to carry out high-performance liquid chromatography (HPLC)... show full transcript
Worked Solution & Example Answer:Consider the following changes that could be applied to the operating parameters for a chromatogram set up to carry out high-performance liquid chromatography (HPLC) with a polar stationary phase and a non-polar mobile phase: I decreasing the viscosity of the mobile phase II using a more tightly packed stationary phase III using a mobile phase that is more polar than the stationary phase Which of the changes would be most likely to reduce the retention time of a sugar in the HPLC? - VCE - SSCE Chemistry - Question 20 - 2020 - Paper 1
Step 1
I decreasing the viscosity of the mobile phase
Answer
Decreasing the viscosity of the mobile phase can enhance the flow rate, allowing the sugar to elute more quickly. This is beneficial as lower viscosity results in reduced resistance to flow, which can potentially decrease retention time.
Step 2
II using a more tightly packed stationary phase
Answer
Using a more tightly packed stationary phase generally increases the interaction between the stationary phase and the analyte, such as sugar. This can lead to an increased retention time, hence it does not contribute to reducing the retention time.
Step 3
III using a mobile phase that is more polar than the stationary phase
Answer
Using a mobile phase that is more polar than the stationary phase will enhance the solubility of polar compounds like sugar in the mobile phase. This will indeed reduce the retention time as the sugar would spend more time in the less interacting mobile phase.