Isotachophoresis and isotachophoresis - zone electrophoresis separations of inorganic anions present in water samples on a planar chip with column-coupling separation channels and conductivity detection

The use of a poly(methylmethacrylate) chip, provided with two separation ch annels in the column-coupling (CC) arrangement and on-column conductivity d etection sensors, to electrophoretic separations of a group of inorganic an ions (chloride, nitrate, sulfate, nitrite, fluoride and phosphate) that nee d to be monitored in various environmental matrices was studied. The electr ophoretic methods employed in;his study included isotachophoresis (ITP) and capillary zone electrophoresis (CZE) with on-line coupled ITP sample pretr eatment (ITP-CZE). Hydrodynamic and electroosmotic flows of the solution in the separation compartment of the CC chip were suppressed and electrophore sis was a dominant transport process in the separations pet-formed by these methods. ITP separations on the chip provided rapid resolutions of sub-nmo l amounts of the complete group of the studied anions and made possible rap id separations and reproducible quantitations of macroconstituents currentl y present in water samples (chloride, nitrate and sulfate). However, concen tration limits of detection attainable under the employed TTP separating co nditions (2-3.10(-5) mol/l) were not sufficient for the detection of typica l anionic microconstituents in water samples (nitrite, fluoride and phospha te). On the other hand, these anions could be detected at 5-7.10(-7) mol/l concentrations by the conductivity detector in the CZE stage of the ITP-CZE combination on the CC chip. a sample clean-up performed in the ITP stage o f the combination effectively complemented such a detection sensitivity and nitrite, fluoride and phosphate could be reproducibly quantified also in s amples containing the macroconstituents at 10(4) higher concentrations. ITP -CZE analyses of tap, mineral and river water samples showed that the CC ch ip offers means for rapid and reproducible procedures to the determination of these anions in water (4-6 min analysis times under our working conditio ns). Here, the ITP sample pretreatment concentrated the analytes and remove d nanomol amounts of the macroconstituents from the separation compartment of the chip within 3-4 min. Both the ITP and ITP-CZE procedures required no or only minimum manipulations with water samples before their analyses on the chip. For example, tap water samples were analyzed directly while a sho rt degassing of mineral water (to prevent bubble formation during the separ ation) and filtration of river water samples (to remove particulates and co lloids) were the only operations needed in this respect. (C) 2001 Elsevier Science B.V. All rights reserved.