Passage the N-Terminus of an Amino Acid Must Be Protected with with 9-Fluorenylmethoxycarbonyl

Passage
The N-terminus of an amino acid must be protected with 9-fluorenylmethoxycarbonyl (Fmoc) during solid state peptide synthesis to avoid side reactions (Scheme I) .
Scheme IThe Fmoc protecting group is typically removed with piperidine (Scheme II) , a heterocyclic secondary amine.
Scheme IIBecause the use of piperidine is restricted, structurally similar amines were examined as possible replacements.  To determine whether piperidine analogues were suitable alternatives for Fmoc removal, deprotection of Compound 2 was carried out with several amine bases (Scheme III) .
Scheme IIICompound 2 was prepared from L-tryptophan and Fmoc-Cl, and the reaction was monitored by thin-layer chromatography (TLC) and visualized by ultraviolet light.  The deprotections were done with piperidine and each analogue using a microwave set to 155 watts at 75 °C for 15 seconds.  The products of the deprotections were analyzed by high-performance liquid chromatography (HPLC) and mass spectrometry; the retention times of the products were compared to tryptophan and Compound 2 standards.
Adapted from O.P. Luna et al, "Deprotection Reagents in Fmoc Solid Phase Peptide Synthesis: Moving Away from Piperidine?." Molecules. ©2016 MDPI.
-If a C18 hydrocarbon HPLC column is used for analysis of the Scheme III reaction results, which of the following solvents would NOT be used for the mobile phase?

A) Acetone
B) Methanol
C) Hexanes
D) Water