If you were using a hydrophobic column instead of a nickel column in your purification set up, what order would the following peptides elute (first to last) at pH7.4 : Peptide X: Arg-Pro-His-Lys-Glu-Asp Peptide Y: Pro-Ile-Val-Gly-Leu-Trp Peptide Z: Val-Pro-Pro-Glu-Asp-Pro-Lys