Construction and analytical application of an on-column photo reactor for improved detection of iron-species as plant metabolites in capillary flow injection and capillary electrophoresis.

An on-column photo reactor for CE, which is constructed from UV-transparent capillaries and a small Pen-Ray UV lamp, is applied to the analysis of small, non-covalent iron-species. These iron-species, e.g. phytosiderophores (PS) in grasses and the non-protein amino acid nicotianamine (NA), play an important role in plant metabolism. The photo reactor is placed directly in front of the on-column absorbance detector, illuminating only some centimeters of the capillary. The photo reactor is used for capillary electrophoresis (CE) and also for capillary flow injection analysis (CFIA). Photoinduced sensitivity changes for model iron-species and for plant extracts are investigated, using UV detection and capacitively coupled contactless conductivity detection (C(4)D). The detection sensitivity for iron-species is enhanced in CFIA; the enhancement factor depends on the type of iron-species. In CE, the sensitivity of iron-species is kinetically dependent on the type of iron-species, decreasing with both detectors, but a photo reaction product is detectable. The relationship between irradiation window length and sensitivity is investigated quantitatively using EDTA-Fe(III). Pure ligands without iron are little affected by the photo reaction in both CFIA and CE. In CE, the detector signals of iron-species in real plant samples are selectively decreased with the proposed photo reactor, thus enabling a simple screening method for such photoactive iron-species.