title: Concurrent high-sensitivity conductometric detection of volatile weak acids in a suppressed anion chromatography system.
abstract: A suppressed hydroxide eluent anion chromatograph effluent flows through the outside of a gas-permeable membrane tube while electrogenerated 100-200 μM LiOH flows through the lumen into a second conductivity detector. Undissociated volatile acid eluites (e.g., H2S, HCN, H2CO3, etc., represented as HA) transfer through the membrane and react as OH(-) + HA → A(-) + H2O; the conversion of high-mobility OH(-) to lower mobility A(-) results in a significant negative response for these analytes. With the chromatograph operated at a macroscale (0.3 mL/min) the LiOH flow can be 3-30-fold lower, resulting in corresponding enrichment of the transferred analyte prior to detection. Because there is no mixing of liquids, the detector noise is very low (<0.1 nS/cm), comparable to the principal chromatographic detector. Thus, despite a background of 25-45 μS/cm, limits of detection for sulfide and cyanide are in the submicromolar level, with a linear dynamic range up to 100 μM. Carbonate/bicarbonate can also be sensitively detected. We demonstrate adaptation in a standard commercial system. We also show that Microsoft Excel-based numerical simulations of transport quantitatively predict the observed behavior well.
authors.affiliation: Department of Chemistry and Biochemistry, University of Texas at Arlington, Arlington, Texas 76019-0065, United States.
authors.forename: Hongzhu
authors.initials: H
authors.lastname: Liao
authors.affiliation: Department of Chemistry and Biochemistry, University of Texas at Arlington, Arlington, Texas 76019-0065, United States.
authors.forename: Akinde Florence
authors.initials: AF
authors.lastname: Kadjo
authors.affiliation: Department of Chemistry and Biochemistry, University of Texas at Arlington, Arlington, Texas 76019-0065, United States.
authors.forename: Purnendu K
authors.initials: PK
authors.lastname: Dasgupta