Molybdenum complexes 8-hydroxyquinoline

Van den Berg [510] carried out direct determinations of molybdenum in seawater by adsorption voltammetry. The method is based on complex formation of molybdenum (VI) with 8-hydroxyquinoline (oxine) on a hanging mercury drop electrode. The reduction current of adsorbed complexions was measured by differential pulse adsorption voltammetry. The effects of variation of pH and oxine concentration and of the adsorption potential were examined. The method was accurate up to 300 nmol/1. The detection limit was 0.1 nmol/1. 

In addition to these reactions, metal ions and ligands may participate in many other equilibria reactions such as complex formation, protolysis, and hydrolysis reactions. In order to transfer metal ions quantitatively into the organic phase, the extraction conditions (pH, reagent concentrations, volume ratio of the liquid phases) must be optimized. Figure 146 represents the response of molybdenum as a function of pH in three different organic solvents with toluene-3,4-dithiol and 8-hydroxyquinoline as ligands. According to this plot the determination of molybdenum is most sensitive in MIBK... 

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. 

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