Ionic chromatographic determination of iodides, nitrites and bivalent iron in water with amperometric detector

Introduction. The majority of ionic chromatographic methods approved in our country for assessing the quality and chemical safety of water for the content of controlled anions and cations are developed using conductometry. However, quantitative determination of micro concentrations of cations and anions in drinking water and other water bodies against the background of macro concentrations of other components due to their interfering influence by the method of conductometric ion-chromatographic analysis is not possible.

Material and methods. The tap water in Nothern East Administrative district of Moscow was used. The “Stayer” ion chromatograph with amperometric and conductometric detectors and separating columns was used. The column Phenomenex Star Ion A-300 100/4.6 was used for the determination of iodide. The column Shodex IC SI-52 4E 250/4, 6 was used for the determination of nitrite. The column Shodex IC YS-50 150/4.6 was used for the determination of bivalent iron.

Results. Chromatograms of ion chromatographic analysis with amperometric and conductometric detections of tap water with different contents of target ions are presented. It is shown that it is impossible to determine the target components using the standard method with conductometric detection. The content of accompanying ions (chlorides, nitrates, and sulfates), exceeding the concentration of nitrite and iodide by tens of thousands of times, was not prevented by the determination.

Discussion. The high efficiency of the proposed method for determining iodides, nitrites, and bivalent iron is provided due to their anode discharge in the electrochemical cell of the detector. Interfering components (chloride, nitrate, phosphate, and sulfate) neither participate in the anodic oxidation process and nor generate an electrical signal; that allows determining micro concentration of nitrite and iodide ions and bivalent iron in virtually any aqueous system containing an excess of chlorides, nitrates, sulfates.

Conclusion. Authors proposed a highly sensitive ion - chromatographic amperometric determination of iodide, nitrite ions and bivalent iron in water and other water bodies. It allows eliminating the interfering influence of macro concentrations of accompanying components. The determination is performed by direct insertion of the sample into the chromatographic system.