I am reading this journal article which discusses using high-performance liquid chromatography (HPLC) to separate dyes from wine. Here are the relevant facts about the experimental setup:
- Two mobile phases are used, a solvent A and a solvent B. Solvent A is is 40% methanol and solvent B is 70% methanol. Both solvents also have 25% 0.02M tetrabutyl-ammoniumhydroxide phosphate solution as well.
- The stationary phase is a LiChrospher 100 RP-18e column.
From the chromatogram, we see that amaranth has the fastest elution time of 6.60 minutes. My questions relate to what inferences can we draw from elution times:
- Does the elution time correlate with the polarity of the compound itself? Here, it states that similarities in polarity correlates positively with elution time. The stationary phase used in this experiment (the LiChrospher) is a nonpolar silica column. Thus, with amaranth coming out the fastest, would it make it the most polar compound?
- Further, how does the use of two solvents (A and B) affect making an inference like the one above? In the chromatogram above (specifically chromatogram "a") and the associated table, the elution time for the three compounds ranged from 6.60 minutes to 9.76 minutes. Since a solvent A and a solvent B were used, how do I know which compounds were eluted by which solvent? (If my interpretation of how the solvents A and B work is wrong, please correct me). Also, how does the use of two solvents affect understanding the relative polarity of the compounds?