Single-run ion chromatographic separation of inorganic and low-molecular-mass organic anions under isocratic elution: Application to environmental samples

摘要

For the isocratic ion chromatography (IC) separation of low-molecular-mass organic acids and inorganic anions three different anion-exchange columns were studied: IonPac AS14 (9 mu m particle size), Allsep A-2 (7 mu m particle size), and IC SI-50 4E (5 mu m particle size). A complete baseline separation for all analyzed anions (i.e., F-, acetate, formate, Cl-, NO2-, Br-, NO3-, HPO42- and SO42-) in one analytical cycle of shorter than 17 min was achieved on the IC SI-50 4E column, using an eluent mixture of 3.2 mM Na2CO3 and 1.0 mM NaHCO3 with a flow rate of 1.0 mL min(-1). On the IonPac AS14 column, it was possible to separate acetate from inorganic anions in one run (i.e.. less than 9 min), but not formate, under the following conditions: 3.5 mM Na2CO3 plus 1.0 mM NaHCO3 with a flow rate of 1.2 mLmin(-1). Therefore, it was necessary to adapt a second run with a 2.0 mM Na2B4O7 solution as an eluent under a flow rate of 0.8 mLmin(-1) for the separation of organic ions, which considerably enlarged the analysis time. For the Allsep A-2 column, using an eluent mixture of 1.2 mM Na2CO3 plus 1.5 mM NaHCO3 with a flow rate of 1.6 mLmin(-1), it was possible to separate almost all anions in one run within 25 min, except the fluoride-acetate critical pair. A Certified Multianion Standard Solution PRIMUS for IC was used for the validation of the analytical methods. The lowest RSDs (less than 1%) and the best LODs (0.02,0.2,0.16,0.11, 0.06,0.05, 0.04, 0.14 and 0.09 mg L-1 for F-, Ac-, For(-), Cl-, NO2-, Br-, NO3-, HPO42- and SO42-, respectively) were achieved using the IC SI-50 4E column. This column was applied for the separation of concerned ions in environmental precipitation samples such as snow, hail and rainwater.