ABSTRACT
A sensitive and selective method was developed for the determination of traces of manganese in urine using on-line electrochemical preconcentration followed by flame atomic absorption spectrometry detection. A home made flow-through polypropylene cell (4.5cm longx0.8cm diameter filled with glass marbles) with an effective inner volume of 0.5ml containing a working and a counter electrode, both of glassy carbon and a Pt pseudo reference electrode was located in a flow injection manifold specially designed for the purpose of this work. The manganese was deposited from buffer solution of NH(3)/NH(4)Cl at pH 9.00 through an oxidizing process at a current of 400mA during 7min. A flow of HCl 0.1moll(-1) at 4mlmin(-1) through the cell, chemically dissolved the deposit. A small portion (15mul) of the concentrate was introduced in a continuously flowing system by means of a timing device and was then carried to the detector for the manganese quantification. All electrochemical and spectroscopic variables as well as possible interferences in both systems were systematically studied. The relative standard deviations for ten consecutive measurements of manganese solutions of 2.0 and 20mugl(-1) were of 2.3 and 1.5%, respectively, while for a sample processed five times was less then 5%. The accuracy of the developed procedure was evaluated by adding known amounts of manganese standard to urine samples and following the whole procedure. Recoveries within the range 97.2-102.8% were obtained. To further prove the accuracy, a Seronorm Trace Elements in Urine, Batch 403125 sample with a reported concentration of 13mugMnl(-1) was also analyzed. The experimental value obtained was of 12.7+/-0.1mugl(-1), which does not differ significantly from the reported amount (p<0.05). A preconcentration factor of 40, a linear range between 0.015 and 60mugl(-1) and a limit of detection of 15ngl(-1) permitted the determination of manganese in real urine samples from non-exposed subjects in the range 0.5-2.8mugl(-1).
