Functionalized Cycloolefin Polymer Capillaries for Open Tubular Ion Chromatography

Abstract

We describe novel cycloolefin polymer (COP)-based open tubular capillary ion exchange columns. COP capillaries (inner diameter of 19-28 μm) were successfully sulfonated at room temperature using a cocktail of ClSOH (85-95% w/w) and HOAc or HSO. The cation exchange capacity is controlled by the sulfonation time and the sulfonation solution composition and can be as high as 300 pequiv/mm. Following sulfonation, the capillaries were coated with 65-nm-diameter anion exchanger (AEX) latex nanoparticles that attach electrostatically. The typical anion exchange capacities were ∼20 pequiv/mm. The chromatographic behavior of the AEX latex-coated COP capillaries are greatly dependent on the degree of sulfonation. When the base is heavily sulfonated, neutrals elute after the anions. The position of the water dip varies with the degree of sulfonation; the elution order is normal (water dip appear before anions) only with lightly sulfonated columns. On silica (-SiOH) or poly(methyl methacrylate) (-COOH) surfaces, AEX latex attachment is not stable over long periods in significant concentrations of strong base (e.g., ≥10 mM NaOH). Latex attachment on sulfonated COP surfaces are much stronger; several types show sufficient binding to be used over long periods at practical eluent concentrations, paving the way for suppressed hydroxide eluent ion chromatography (IC), which is discussed in a companion paper. Another interesting feature of COP capillaries lies in their flexibility. If softened at modestly elevated temperatures (e.g., boiling water), they can be coiled down to <1 mm coil radii, revealing, for the first time, the beneficial effects, albeit small, of centrifugal force on mass transfer in open tubular columns.

Admittance Scanning for Whole Column Detection

“…For chromatographic experiments, capillaries were coated with AS18 latex (COP capillaries were sulfonated before coating); details of COP column preparation appear elsewhere. 21 The OT column injection system used for the capillary columns has been previously described. 13 Figure 1 inset indicates how this injection system is built around the capillary holding tee.…”

Electrodialytic Capillary Suppressor for Open Tubular Ion Chromatography

“…A 19-μm-diameter COP capillary was sulfonated by chlorosulfonic acid (Acros, www.acros.com) to a capacity of ∼3 peq/mm 2 , and then coated with anion-exchange AS18 latex nanoparticles (65 nm in diameter, courtesy of Thermo Fisher Scientific) that attach to the sulfonated capillary walls electrostatically, to be used as the separation column. 16 The anion exchange capacity was 25 peq/mm 2 . [Note: throughout the paper, peq denotes picoequivalent.]…”

“…A hydroxide eluent compatible cyclic olefin polymer (COP) capillary column is reported in a companion paper. 16 There are no extant suppressor designs that can be adapted to these columns with inner bores of 20−30 μm without introducing significant extra column broadening. A very low-volume, low-dispersion suppressor with sufficient suppression capacity is a critical requirement.…”

Investigating the Effect of Column Geometry on Separation Efficiency using 3D Printed Liquid Chromatographic Columns Containing Polymer Monolithic Phases

“…9,10 However, to the best of our knowledge, only one practical study has been reported todate on the effects of column 3D geometry on retained solutes using liquid chromatography, which was a recent brief study investigating an open-tubular coiled anion exchange functionalized cycloolefin polymer capillary column. 11 Although relatively minor, the coiled column exhibited reduced b and c terms in relation to a straight capillary column of similar functionality and dimensions.…”

“…Therefore, interest remains for experimental investigation of such effects, albeit with limitations on what can be practically achieved using traditional column formats. Experimental observations have been discussed previously in relation to both gas chromatography − and supercritical fluid chromatography. , However, to the best of our knowledge, only one practical study has been reported to-date on the effects of column 3D geometry on retained solutes using liquid chromatography, which was a recent brief study investigating an open-tubular coiled anion exchange functionalized cycloolefin polymer capillary column . Although relatively minor, the coiled column exhibited reduced b and c terms in relation to a straight capillary column of similar functionality and dimensions.…”