Speciation and preconcentration of vanadium(V) and vanadium(IV) in water samples by flow injection-inductively coupled plasma optical emission spectrometry and ultrasonic nebulization

WUILLOUD, RODOLFO G.

Florianópolis

Simposio; SEVENTH RIO SYMPOSIUM ON ATOMIC SPECTROMETRY; 2002

SEVENTH RIO SYMPOSIUM ON ATOMIC SPECTROMETRY

The chemicals and physical properties of a metal species depend very much on its oxidation state; hence an accurate determination of each species is important to evaluate both the potencial risk and benefits of some metals. Vanadium has many oxidations states and ionic forms in aqueous solution. It exists in two different oxidation states, V(V) and V(IV), in  well aerated natural and industrial Waters. The significance of V speciation is that the two oxidation states have different nutritional and toxic properties. The toxicity of V is dependent on its oxidation state, with V(V) being more toxic than V(IV). Otherwise, the insulin-like properties of V, especially its effects on mitogenesis, suggest that the element plays a role in growth and development. Therefore speciation and determination of V is receiving increasing attention in pollution and nutritional studies.Since one of the routes of incorporation of V into the human body is water, its determination in this type of samples becomes very important. The concentration of V in natural water is very low, in the order of a few ug/L, therefore powerful techniques are required and only few of them show sufficient sensitivity. In order to achieve accurate, reliable and sensitive results, preconcentrations and separations are needed when the concentrations of analyte elements in the sample are too low to be determined directly by inductively coupled plasma optical emission spectrometry (ICP-OES).In this work,an on-line vanadium(IV) and vanadium(V) separation, preconcentration and determination system comprising with ICP-OES coupled to a flow injection (FI) method with ultrasonic nebulization (USN) system was studied. The vanadium species were retained on an Amberlite XAD-7 resun as vanadium-2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (V-5-Br-PADAP) complex, at pH 3.7. Elevated selectivity was obtained with the combined use of formation on-line of the complexes and 1,2-cyclohexanediaminetetracetic acid (CDTA) as masking agent. The vanadium complexes were removed from the micro-column with 30% v/v nitric acid. A sensitivity enhancement factor of 225 was obtained with respect to ICP-OES using pneumatic nebulization (15 for USN and 15 for microcolumn). The value of detection limit for the preconcentration of 10 mL of aqueous solution was 19 ng/L. The precision for 10 replicate determinations at the 5-ug/L V level was 2.3% relative standard deviation (RSD), calculated from the peak heights obtained. The calibration graph using the separation and preconcentration system for vanadium species was linear with a correlation coefficient of 0.9992 at levels near the detection limits up to 100 ug/L. The method was successfully applied to the speciation analysis of vanadium in river water samples.