Indefinite. Restriction lift date: 10000-01-01
New thin shell silica particles and HILIC phases for liquid chromatography: synthesis, characterisation and functionalisation
Langsi, Victor K.
University College Cork
For the past decade, there has been a steady growth of interest in the use of superficially porous particles with a solid core and a porous shell (also known as fused core, core-shell or porous shell) for fast and highly efficient separation of low molecular weight solutes to large and complex analytes, while avoiding excessive back pressure. In this work, four different sub-2µm thin shell particles were synthesised by the seeded growth method: Three with shell thickness of 50nm were designated as TS1.5-50 (solid core 1.4µm), TS1.7-50 (solid core 1.6µm) and TS1.9-50 (solid core 1.8µm); and the fourth with 100nm shell layer as TS1.7-100 (solid core 1.5µm). A sub-2µm core shell particle (solid core 1.4µm, 150nm shell layer) was also synthesised for comparison and designated as EiS1.7-150. All the unmodified shell particles were characterised by SEM, TEM, DLS (dynamic light scattering) and BET analyses. The thin shell particles TS1.5-50, TS1.7-50 and TS1.9-50, including the core shell particle EiS1.7-150 were chemically functionalised with C18 ligand. A new zwitterionic N-alkyl betaine stationary phase containing quaternary ammonium ion and carboxylate ion groups was also functionalised on a 3.0µm porous silica particle (ExsilTM pure) by silane chemistry and further quaternisation with sodium chloroacetate for HILIC separation of polar analytes. All bonded phase materials were characterised by microanalysis, thermogravimetric analysis (TGA) and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. The bonded thin shell and core shell particles were slurry packed in narrow bore columns (2.1mm ID x 50mm) and labelled as TS1.5-50-C18, TS1.7-50-C18, TS1.9-50-C18 and EiS1.7-150-C18 respectively. Kinetic studies performed on the bonded thin shell columns using naphthalene and 55% acetonitrile in water yielded retention coefficients in the range 1.26-1.35 and 5.6 for the core-shell particle and minimum reduced plate height range from 3.89-4.26 for the thin-shell particles and 2.03 for the core-shell particle. The unmodified TS1.7-100 particle packed in 4.6mm ID x 100mm column was applied as a HILIC stationary phase for rapid determination (< 1min) of uric acid and creatinine in human urine samples giving calculated concentrations in the range 782-1206 µg/mL and 535-862µg/mL respectively. Percentage recoveries of uric acid and creatinine were evaluated between 86.7-92.1% and 92.7-94.3% and the limit of detection (LoD) at 0.03µg/ml and 0.05µg/ml respectively. The resulting N-alkyl betaine bonded material packed in 4.6mm ID x 100mm column and labelled as Nab-HILIC was investigated for HILIC selectivity characteristics using the Tanaka testing method and the results revealed close selectivity properties with the commercially available ZIC®-HILIC column containing sulfobetaine stationary phase. The effects of pH, buffer concentration and organic solvent composition changes on retention and selectivity were investigated using anionic, cationic and zwitterionic analytes to decipher the retention mechanisms of different polar analytes on the new stationary phase using HILIC mode. Nab-HILIC column evaluation and measurement of nonreduced HETP using homovanillic acid (HVA), 5-hydroxytryptamine (5-HT) and cytosine (CS) was performed with resulting retention coefficients of 0.52, 0.93 and 1.53 respectively and non-reduced HETP (H) of 5.8, 9.1 and 6.7 respectively compared to 14.2, 4.3 and 4.7 for ZIC®-HILIC column.
Thin shell particles , Sub-2 um silica , Seeded growth , Hydrophilic interaction liquid chromatography , Selectivity , Zwitterionic N-alkylbetaine silica phase
Langsi, V. 2017. New thin shell silica particles and HILIC phases for liquid chromatography: synthesis, characterisation and functionalisation. PhD Thesis, University College Cork.