A new bonded silica based on an amino acid derivative as a TLC stationary phase to solve nitrophenol structural isomerism and ibuprofen stereoisomerism

Abstract

Abstract Background Many amino acids and their derivatives have been used previously as chiral selectors in thin layer chromatography. Herein, we reported the synthesis, characterization, and chromatographic evaluation of a new modified stationary phase based on (S)-3-(aminomethyl)-5-methylhexanoic acid (also known as pregabalin) as an amino acid ligand bonded to the silica surface via triazine attachment. Results SC-2P (silica-cyanuric-2-pregabalin) is a bonded silica stationary phase prepared by direct binding of the pre-synthesized cyanuric-2-pregabalin organic ligand on the chlorinated silica surface. FT-IR and UV diffuse reflection spectroscopy (UV-DRS) were used to characterize the synthesized bonded phase, and the specific surface area was determined using the methylene blue Langmuir isotherm method to be 147.04 m2/g. TLC plates were prepared from a slurry of this synthesized material with 2 mM of Cu2+ as a selector additive, and the chromatographic characteristics of these plates were investigated to separate a ternary mixture of o-, m-, and p-nitrophenol as structural isomers, and a racemic mixture of (±)-ibuprofen as stereoisomers. Solvent systems of n-hexane:dichloroethane:n-propanol (75:20:5, v/v/v) and Dichloroethane:acetonitrile (90:10, v/v) were selected as mobile phases for nitrophenol and ibuprofen mixtures, respectively. The successful separation was densitometrically confirmed, and retardation factors (R f) were determined for o-, m-, and p-nitrophenol at 320 nm to be 0.83, 0.45, and 0.28, and for R(−)-, S(+)-ibuprofen at 220 nm to be 0.43 and 0.63, respectively. Conclusion The synthesis, characterization, and chromatographic evaluation of SC-2P were reported in this article. SC-2P was used with copper ions to form in situ ligand exchange reagent (LER), which was successfully employed to solve an isomeric mixture of nitrophenol and a racemic mixture of (±)-ibuprofen. The synthesized stationary phase showed high repeatability with minimum R f shifts between batches.

Keywords

• Thin layer chromatography
• Stationary phase
• Bonded silica
• Ligand exchange reagent
• Chiral selector
• Enantioseparation