Determination of lead isotope ratios in port wine by inductively coupled plasma mass spectrometry after pre-treatment by UV-irradiation Original Research Article

A suitable method for determination of the Pb isotope ratios in Port wine by inductively coupled plasma mass spectrometry (ICP-MS) has been developed and applied to 24 Port wine samples of different ages and characteristics. The samples were pre-treated by UV-irradiation (mercury high pressure vapour lamp, 1000 W) for 1.5 h. Before ICP-MS measurements the samples were filtered (0.45 μm pore size) and 10 times diluted with a 0.5% HNO3 solution. Two different types of mass bias correction in the ICP-MS determinations were used for comparison purposes: (i) external correction with a Pb isotopic standard solution and (ii) internal correction with Tl as internal standard. No significant differences were found between the results obtained with the two types of corrections, both methods being suitable for mass bias correction in the present experimental conditions. The relative standard deviations associated to the mean values of the Pb isotope ratios were of about 0.3% for 207Pb/206Pb and for 208Pb/206Pb and about 0.8% for 204Pb/206Pb. Such precisions showed to be sufficient to differentiate natural variations of the Pb isotope abundances in Port wine samples. Significant correlations (p < 0.05) were found between the 207Pb/206Pb or the 204Pb/206Pb ratios and the age of the Dated Port wines. The total Pb concentration were also determined by atomic absorption spectrometry with electrothermal atomisation. The Pb concentrations varied from 47 to 804 μg l−1. A significant decrease (p < 0.05) of the Pb concentration with the age of the wine was observed, as also as a significant correlation (p < 0.05) between the total Pb concentration and the 208Pb/206Pb ratio.