Trace determination of iron in water at the mu g/1 level by on-line coupling of capillary isotachophoresis and capillary zone electrophoresis with UV detection of the EDTA-Fe(III) complex

The determination of iron in water at the trace level by on-line coupled capillary isotachophoresis and capillary zone electrophoresis (CITP-CZE) with a commercial column coupling device is described. Iron is determined as the negatively charged complex with EDTA which is highly UV-absorbing and thus enables photometric detection at 254 nm. The analyses are performed using 10 mmol/l HCl+20 mmol/l L-histidine+0.1% hydroxypropylmethyl cellulose (pH 6.0), 5 mmol/l MES, and 25 mmol/l MES+10 mmol/l bis-tris-propane (pH 6.6) which served as leading, terminating and background electrolyte, respectively. Samples are acidified with HNO3, diluted and EDTA added (to a final concentration of 10(-4) mol/l) prior to CITP-CZE analysis. The detection limit of Fe(III) is 10 mu g/l, and is given by the chemical noise due to the impurities of the chemicals used enriched by the ITP preconcentration step. The precision of the CE measurement, expressed by the relative standard deviation, is about 3% (at the 400 mu g/l level); the recovery is between 80 and 115% depending on the iron concentration level (40-400 mu g/l).