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Electrodialytic Capillary Suppressor for Open Tubular Ion Chromatography Weixiong Huang, and Purnendu K. Dasgupta Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.6b03667 • Publication Date (Web): 14 Nov 2016 Downloaded from http://pubs.acs.org on November 17, 2016
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Analytical Chemistry
Electrodialytic Capillary Suppressor for Open Tubular Ion Chromatography Weixiong Huang, Purnendu K. Dasgupta* Department of Chemistry and Biochemistry, The University of Texas at Arlington, Arlington, Texas 76019-0065, United States
* E-mail:
[email protected]. Fax: 817-272-3808.
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Analytical Chemistry
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ABSTRACT We describe an electrodialytic capillary suppressor for suppressed conductometric open tubular ion chromatography (SC-OTIC). For practical eluent concentrations, suppressor active lengths 3 orders of magnitude less than the eluent concentration). Nonsuppressed ion chromatography (NSIC)) relies on the difference in the equivalent conductance of the eluent (E-) and the analyte ions (A-).But the sensitivity is poor as the difference (A- - E-) is small and the noise is high because the background is high. A suppressor serves to convert the eluent to a very weak electrolyte (weak acid/base or water), greatly reducing (suppressing) the background conductivity while the analyte signals are enhanced because their counterions are substituted by more conductive hydronium or hydroxide ions. Thus, by reducing the background (and thence noise level) by ~ 2 orders of magnitude and improving the sensitivity by nearly an order of magnitude, the limits of detection (LODs) are improved by 2 ~ 3 orders of magnitude. A variety of suppressors have emerged, from early packed-column,1 hollow-fiber,3,4 and micromembrane suppressors,5 to the current electrodialytic membrane-based,6,7 and continuously regenerated packed-column suppressors.8 Postcolumn addition of colloidal ion exchangers9 and microfluidic or like suppressors have also been described.10-12 By exploiting electrolytic decomposition of water to generate the hydronium/or hydroxide ions necessary for suppression reactions, an electrodialytic membrane-based suppressor can be operated in self-regenerating mode without addition of any regenerant, and permits high dynamic suppression capacity in a low holdup volume.
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Capillary ion chromatography (CIC) is gaining attention because of its low sample and eluent consumption, as well as high efficiency. SCIC was first demonstrated by Rokushika et al.13 A fused-silica separation column (0.19 mm i.d.) was coupled to a sulfonated hollow fiber tubing (0.2 mm i.d. x 10 mm). Before the commercial introduction of packed capillary (0.4 mm i.d.) IC, our laboratory demonstrated a portable packed capillary (0.18 mm i.d.) IC using a 1.9 cm length of a 50 m i.d., radiation grafted sulfonated PTFE tube as a chemically regenerated suppressor.14 The last review on CIC is now 12 years old.15 We have pursued suppressed conductometric open tubular ion chromatography (SCOTIC) for some time. 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 m without introducing significant extra column broadening. A very low-volume, low-dispersion suppressor with sufficient suppression capacity is a critical requirement. Integration of the suppressor and detector17 can reduce postsuppressor broadening but does little for broadening in the suppressor and leaves the issue of dispersion in any connection between the suppressor and the detector unaddressed. Strategies previously used to reduce dispersion in macroscale suppressors, such as packing perfluorosulfonate cation exchanger (Nafion) tubing with inert beads,18 filling with nylon monofilament,Error! Bookmark not defined. etc. do not seem applicable in this scale. As an ionically conductive cation-exchanger, Nafion has had a long history of use in fabricating suppressors.12,13,18 Herein, we describe a Nafion-based electrodialytic suppressor of
