Determination of trace amounts of cobalt in foods by polymer-phase fluorophotometry with thiamine

A selective and sensitive method for the determination of trace amounts of cobalt has been developed by polymer-phase fluorophotometry with thiamine as an emission reagent. The method is based on the fact that cobalt reacts with thiamine to form a strong fluorescent compound in 0.65% sodium hydroxide medium. The fluorescence intensities show a good linearity with the concentration of cobalt in the range of 2–56 μg/L. The fluorescence intensities were measured in 5-mm quartz cells with excitation and emission wavelengths at 375 and 438 nm, respectively. The detection limit is 0.61 μg/L and the RSD is 1.70%. The sensitivity of the method is four times the conventional fluorophotometry in solution. The fluorescent life of thiamine is longer in polymer than that in solution. The general coexisting ions have no interference to the reaction of cobalt and thiamine except for copper and iron ions. The proposed method was applied to the determination of trace amounts of cobalt in food samples with satisfactory results.