Polystyrene -co- Divinylbenzene PolyHIPE Monoliths in 1.0 mm Column Formats for Liquid Chromatography

Abstract

The reversed phase liquid chromatographic (RP-HPLC) separation of small molecules using a polystyrene-co-divinylbenzene (PS-co-DVB) polyHIPE stationary phases housed within 1.0 mm i.d. silcosteel columns is presented within this study. A 90% PS-co-DVB polyHIPE was covalently attached to the walls of the column housing by prior wall modification with 3-(trimethoxysilyl) propyl methacrylate and could withstand operating backpressures in excess of 200 bar at a flow rate of 1.2 mL/min. Permeability studies revealed that the monolith swelled slightly in 100% acetonitrile relative to 100% water but could nevertheless be used to separate five alkylbenzenes using a flow rate of 40 µL/min (linear velocity: 0.57 mm/s). Remarkable column-to-column reproducibility is shown with retention factor variation between 2.6% and 6.1% for two separately prepared columns.

Keywords: isocratic separation; microbore; polyHIPE; polystyrene; reversed phase LC; silcosteel.

Figure 1

GMA-co-EDMA polyHIPE with (a) 4.5% surfactant; and (b) 5.5% surfactant. A GMA-co-EDMA polyHIPE with 4.5% surfactant was formed in (c) unmodified 0.76 mm i.d. PEEK; and (d) GMA-modified 0.76 mm i.d. PEEK.

Figure 2

PS-co-DVB polyHIPE (90% porosity) formed within 1.0 mm i.d. silcosteel tubing (a); edge magnification of Image (a) showing binding to the column wall (b); typical polyHIPE morphology in the column centre (c); image of the parent, free-standing polyHIPE (d).

Figure 3

Backpressure profiles of PS-co-DVB polyHIPE monoliths in silcosteel tubing for water (a); methanol (b); and acetonitrile (c). Blue plots represent Column #1 and green plots represent Column #2. Backpressure measurements were made in triplicate at each flow rate.

Figure 4

Isocratic separation of alkylbenzenes on PS-co-DVB polyHIPEs. (a): Column #1, (b): Column #2. Chromatographic conditions: Column: 1.0 mm × 100 mm 90% porosity PS-co-DVB polyHIPE, Mobile phase: 50% ACN, Flow rate: 40 µL∙min⁻¹, Injection volume: 1 µL, Detection: UV at 214 nm. Peak assignments: (1) toluene, (2) ethylbenzene, (3) propylbenzene, (4) butylbenzene, (5) pentylbenzene. All analytes are 0.1 mg∙L⁻¹.