On-line preconcentration and speciation analysis of inorganic vanadium in urine using L-methionine immobilized on controlled pore glass. Determination by UN-ICP OES.

PABLO H. PACHECO, RAÚL A. GIL, ROBERTO A. OLSINA, LUIS D. MARTINEZ, PATRICIA SMICHOWSKI.

Rio de Janeiro, Brasil

Simposio; Tenth Rio Symposium on Atomic Spectroscopy; 2008

A study was undertaken to ascertain the analytical capabilities of combined ICP OES with ultrasonic nebulization to perform on-line preconcentration and speciation of inorganic V species in urine samples using a micro-column packed with L-methionine immobilized on controlled pore glass (CPG) as solid phase extractant. Vanadium is widely distributed in the earth’s crust but in low abundance. Environmental pollution caused by vanadium is almost entirely due to industrial activities, such as the production of steel, pigments, photographic materials and insecticides. Vanadium is also released on oil combustion. Vanadium at trace amounts is beneficial to normal cell growth, being one of the so-called essential elements. It can exist in many oxidation states from – 1 to + 5 and in a number of oxoanionic and oxycationic forms. V(V)is more toxic than V(IV).   For a comprehensive exposure study, knowledge of V levels in urine is required to ascertain any relationship to exposure, been V used as a biomarker. Quantification of trace levels of vanadium in biological fluids is a difficult analytical task, due not only to the very low analyte concentrations that need to be addressed, but also by the relatively complexity of the matrix. Inductively coupled plasma optical emission spectrometry (ICP OES) has been extensively used for the determination of traces of V, but the low levels of V in urine are not compatible with the detection limits of these techniques. Preconcentration is an effective means for extending the detection limits of ICP OES technique. New substrates such as aminoacids and poly-aminoacids chains have been successfully used for metal retention, separation, preconcentration and/or speciation. At pH 5.0, L-methionine is selective only towards V(V) while, total vanadium was quantitatively adsorbed by the solid phase at pH 9.0 [as V(V)] due to V(IV) oxidation in alkali media. Vanadium species retained by L-methionine were quantitatively eluted from the column with 10% HCl. Effects of acidity, sample flow rate, concentration of eluent and interfering ions on the recovery of the analytes have been systematically investigated. The detection limit (3ó) of V is 0.008 ng mL−1 for USN–ICP-OES with an enhancement factor of 900 (10 for USN and 90 for L-methionine), and the relative standard deviation (R.S.D.) is better than 2%. The proposed method has been applied to the determination of inorganic V(V) and V(IV) in urine. The method is simple, no masking agents are necessary, no oxidation/reduction is required, and only by adjusting the pH both species are preconcentrated and determinated in complex matrix as human urine.