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Issue 12, 2017
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High pH instability of quaternary ammonium surfactant coatings in capillary electrophoresis

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Abstract

The two-tailed cationic surfactant dioctadecyldimethyl ammonium bromide (DODAB) produces semi-permanent coatings that yield strongly reversed electroosmotic flow (EOF), for example −0.31 ± 0.01 cm2 kV−1 s−1 at pH 3.5. Moreover, these coatings are easy to prepare, regenerable, cost effective, and yield high efficiency (520 000–900 000 plates per m) separations of cationic proteins over many runs under acidic (pH 3.5) conditions. Given the quaternary amine functionality of DODAB, we were surprised to observe that DODAB coatings become unstable at pH > 7. At pH 7.2, the EOF of a DODAB coated capillary drifted from reversed to cathodic over only 5 runs, and protein separations became severely compromised. By pH 12, no EOF reversal was observed. Electrophoretic and mass spectrometric studies demonstrate that the coating decomposition involves a surface conversion of the quaternary amine in DODAB to a variety of products, although the exact mechanism remains elusive. Regardless, the results herein demonstrate that semi-permanent coatings based on cationic two-tailed surfactants such as DODAB are limited to separations using acidic buffers.

Graphical abstract: High pH instability of quaternary ammonium surfactant coatings in capillary electrophoresis

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Publication details

The article was received on 23 Feb 2017, accepted on 06 May 2017 and first published on 10 May 2017


Article type: Paper
DOI: 10.1039/C7AN00330G
Citation: Analyst, 2017,142, 2145-2151
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    High pH instability of quaternary ammonium surfactant coatings in capillary electrophoresis

    L. Shulman, L. Pei, M. F. Bahnasy and C. A. Lucy, Analyst, 2017, 142, 2145
    DOI: 10.1039/C7AN00330G

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