ICP-MS determination of strontium isotope ratio in wine in order to be used as a fingerprint of its regional origin

A suitable methodology for determination of the Sr isotope ratio Sr-87/Sr-86 in wines by inductively coupled plasma mass spectrometry (ICP-MS) has been developed and applied to ten samples of table and fortified wines, from five different Portuguese regions and one from a French region. After a sample pre-treatment (optimised previously) by UV irradiation and a three times dilution with de-ionised water, the solution was submitted to a two-step cation-exchange chromatographic separation for efficient elimination of Rb interference. A 2.5 M HCl solution was used as eluent at a flow rate of about 1 mi min(-1). In the first separation step (the pH of introduced sample was about 4) most of the Rb was removed with the first 120 mi of eluent. The next 40 mi were collected and introduced again to the column without pH neutralisation (pH about zero). In this second separation step, the retention volumes were lower. The Sr-containing fraction (collected between 80 and 120 mi elution volumes) was used for Sr-87/Sr-86 determination by ICP-MS. For such a purpose, the solution was evaporated to near dryness, converted into the nitrate form by addition of 1 mi of concentrated HNO3 and evaporated again to near dryness. Finally, the residue was taken up in 5 mi of de-ionised water and diluted to 15 mi using 0.5% HNO3. Instrumental and sample induced mass bias corrections were required for accurate isotope ratio (IR) determinations. Either external correction with an Sr isotopic standard solution or correction using the value of the Sr-88/Sr-86 ratio (internal correction) was used for that purpose. Both were suitable under the present experimental conditions. The precisions of the Sr IR obtained in wines using the proposed method (relative standard deviations <0.3%) were sufficient to distinguish the Sr isotopic composition in wines from different regions. Therefore, the results suggest that the Sr-87/Sr-86 ratio is a promising fingerprint of wine origin.