On-line dialysis as a sample preparation technique for ion chromatography.

The use of on-line dialysis as a sample preparation technique for ion chromatography is described. A fully automated sample preparation device coupled to an ion chromatographic system for the determination of anions and cations in various matrices is presented. The method was based on stopped-flow dialysis, where the samples were continuously dialyzed for 10 min while the acceptor solution was stationary within the recipient channel. The matrices examined, without additional sample treatment, included milk, untreated wastewater, fruit juice, engine coolant, and a multivitamin tablet. The analyte recoveries for anions and cations in various matrices ranged from 87 to 106%. In addition, multiple sample injections were performed and repeatabilities were found in the range of 0.2 to 4%.

Ion chromatographic determination of acidity.

The practice of determining acid concentrations by titrations has remained unchanged for more than a century. We introduce a new approach to the determination of acid concentrations based on cation exchange chromatography. We demonstrate the ability of sulfonated styrene-divinylbenzene based stationary phases to separate the hydrogen ion from other monovalent cations. The eluent is a dilute solution of a neutral salt, sometimes containing a small concentration of the corresponding acid, e.g., sodium ethanesulfonate, pH adjusted with ethanesulfonic acid. The high equivalent conductance (approximately 350 S.cm2/equiv) of H+ and relatively low eluent concentration allows sensitive conductometric detection of H+, down to the 50 microM level under favorable conditions. The conductometric response to H+ can be linear over a wide range of H+ concentrations, from sub-millimolar to several molar concentrations. The system allows the rapid quantitation of strong acids; weak acids can also be determined depending on pKa and injected concentration. The determinations of several strong and weak acids are presented along with factors that govern their chromatographic analysis.