An amine introduction device, placed after a conventional suppressed conductivity detector in a anion chromatography system based on hydroxide eluent, converts the suppressed eluites from the acid form to an ammonium salt (NR3 + HX ? NR3H+ + X-). Diethylamine is chosen as the amine source due to its low pKb value (pKb 2.91) and high vapor pressure. A conventional suppressed anion chromatography system produces a poor response for very weak acids (pKa >7), if at all, because HX is hardly ionized. A second conductivity detector then measures the conductivity again. The eluites are thus detected against a low diethylamine background (typically 20-30 �S/cm) as negative peaks, because the equivalent conductance of OH- is greater than X-. The performances of the amine introduction device were evaluated with respect to induced dispersion and background noise. The introduction of diethylamine in the vapor phase directly through a permeable membrane actually is superior to solution phase NaOH introduction. Relative to a microelectrodialytic NaOH generator in our previous studies, the amine introduction device is much easier to build. The availability of such a device is expected to facilitate the use of 2-D detection.

2D detection in ion chromatography: Sequential conductometry after suppression and diethylamine introduction

247th National Meeting (2014)

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