Vanadium, analytical methods concentration

The environmental scientist has at his disposal a variety of sensitive, multi-elemental analytical methods that can lead to a massive amount of data on airborne metals. Optimum use of these tools for environmental monitoring calls for focusing resources only on those metals that are environmentally important. Considerations of toxicity along with their ability to interact in the air, leading to the formation of secondary pollutants, and their presence in air have led to the identification of 17 environmentally important metals nickel, beryllium, cadmium, tin, antimony, lead, vanadium, mercury, selenium, arsenic, copper, iron, magnesium, manganese, titanium, chromium, and zinc. In addition to the airborne concentration, the particle size of environmentally important metals is perhaps the major consideration in assessing their importance. 

Vanadium concentrations in blood, serum or urine are used as a biological indicator of exposure to vanadium. Urine and serum are the specimens with widest application and greatest practicability for monitoring human exposure to vanadium compounds, but urine is preferred as an indicator medium. Blood vanadium appears to be a less sensitive indicator than urinary vanadium, partly because the differences in concentrations are hardly appreciable at low levels of exposure with the analytical methods available (Alessio et al., 1988). 

Much work on liquid metal velocity has been done with sodium and serves to illustrate its influence on corrosion. Bagnall and Jacobs [21] have attempted to unify the available data in the literature and correlate corrosion rate with temperature. Sodium velocity and oxygen were the two major variables taken into consideration. With oxygen interpreted on the vanadium wire equilibration scale, it was shown statistically that corrosion rate, R, was independent of velocity above about 3 m/s and directly proportional to oxygen concentration. An example of this correlation is shown in Fig. 4 where the variation of R with oxygen is plotted for type 316 stainless steel at 700°C. Data obtained at very low oxygen levels (<0.5 ppm by vanadium wire) deviate horn the predictive curve. At these low concentrations, mass loss appears to approach the model developed by Weeks and Isaacs [4]. Such behavior is not unreasonable since it is clear that mass loss will, in 2my event, not drop to zero at zero oxygen. Also, an approximate correlation between the vanadium wire scale and vacuum distillation values is shown on the abscissa. Note that the latter scale is not linear and that the vacuum distillation analytical method becomes insensitive below about 5 ppm. 

V0x/Zr02 catalysts were designated as ZVx(y)pHz, where x gives the analytical vanadium content (weight percent), y specifies the preparation method (a, adsorption, i, impregnation or acac, acetylacetonate) and z the AV solution pH. The V-content was determined by atomic absorption (Varian Spectra AA-30) after the sample had been dissolved in a concentrated (40%) HF solution. 

The within-series imprecision of the method is 2% for an average vanadium concentration of 10.2 figlL. The mean recovery rate was calculated to 97.5% and the analytical detection limit calculated as three times the standard deviation of the blank around 1 fig/L. Parallel determinations of the urine samples with an adsorptive inverse voltammetric method (Seiler, 1993) resulted in a coefficient of correlation of 0.992 (y = l.03 x - 0.17), the comparison with the ICP-OES method (Schramel, 1994) a correlation coefficient of 0.986 (y = 0.96 x 4- 1.97) in a concentration range from 1 to 25 fig/L (Fleischer et al., 1991). 

The lUPAC (International Union for Pure and Applied Chemistry) reference method for the determination of nickel in serum and urine [43], for example, recommends an acid digestion followed by extraction with APDC-MIBK prior to ETAAS determination. Similar procedures were described for molybdenum in blood plasma which was extracted as the 8-hydroxyquinoline complex prior to its determination by ETAAS [44] and for vanadium in serum and urine [45]. There is no question, however, that these procedures require skilled operators. As multistage manual procedures they also bear the risk of analyte loss and/or contamination, so that the final result may not always reflect the analyte concentration in the original sample. 

Environmental samples offer a challenge to the analytical chemist because of the matrices involved. These include, among others, fresh- and seawater, sediments, marine and biological specimens, soil, and the atmosphere. For determining trace concentrations of vanadium in these complex matrices, preconcentration and separation techniques may be required prior to instrumental analysis. Hirayama et al. [14] summarize the various preconcentration and separation techniques including chelation, extraction, precipitation, coprecipitation, ion exchange in conjunction with the instrumental method of spectrometry, densitometry, flow injection, NAA, AAS, X-ray fluorescence, and inductively coupled plasma atomic emission spectrometry (ICPAES). While NAA offers great sensitivity and selectivity, its application is limited by the number of research reactors available worldwide. 

Test Method B—Sample is diluted with an organic solvent to give a test solution containing either 5 % (m/m) or 20 % (m/m) sample. The recommended sample concentration is dependent on the concentrations of the analytes in the sample. For the determination of vanadium, interference suppressant is added to the test solution. The test solution is nebulized into the flame of an atomic absorption spectrometer. A nitrous oxide/acetylene flame is used for vanadium and an air/acetylene flame is used for nickel and sodium. The measured absorption intensities are related to concentrations by the appropriate use of calibration data. 

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