Determination of ultra trace concentrations of selenium using the GFAAS technique following on-line electrochemical pre-concentration on a gold-coated porous carbon electrode

In this work the possibility of determination of selenium in water samples was studied by on-line coupling of electrochemical pre-concentration flow through unit and GFAAS. The pre-concentration unit was created from a commercial electrochemical flow through analyser EcaFlow (Istran Ltd.) and a special two-electrode electrochemical flow through cell. The pre-concentration cell consisted of a working electrode made of gold-coated porous carbon and auxiliary electrode made of a Pt-wire. The pre-concentration unit was connected with electrothermal atomisers through 6-way valve with sampling loop. Using the proposed on-line coupling the limit of detection reached 0.01 μg L−1 for a 10 mL sample. The total linear range was between 0.03 and 10 μg L−1. From the number of ions tested only PO 4 3 − ions reduced the signal by about 10% for 50-fold excess. Using this method it was possible to determine Se (IV) or the total inorganic selenium following reduction of Se (VI) by boiling the sample in HCl. The procedure was validated by analysing reference materials and a variety of water samples. A good agreement with the results of ICP-MS was achieved for all samples.