Precise 87Sr/86Sr isotope ratio measurement by quadrupole based ICP-MS after ion exchange separation of Rb for provenance determination of agricultural products

• Main Author: Vorster, Clarisa
• Published: 2010
• Subjects: Wine and wine making; Strontium isotopes; Inductively coupled plasma mass spectrometry; Ion exchange chromatography; Provenance trials
• Online Access: http://hdl.handle.net/10210/3158

M.Sc. === The strontium isotope ratio 87Sr/86Sr in the wine and soil of four wine-producing regions in South Africa has been determined using quadrupole ICP-MS. Isotope ratio measurements with fairly good precision had been obtained and 87Sr/86Sr ratio values in wine and soil samples were statistically evaluated to determine whether the regions investigated could be distinguished. Statistical interpretation of data revealed that the Robertson wine-producing region could be distinguished from Stellenbosch, Swartland and Walker Bay wine regions on the basis of their 87Sr/86Sr ratio. By using a combination of 87Sr/86Sr and multielement data, canonical discriminant functions with very good classification abilities could be obtained to correctly distinguish between wine and soil samples originating from a specific production region. Due to the isobaric overlap of strontium and rubidium at mass 87, a very good strontium-rubidium separation method had to be developed. The chelating properties of EDTA and DCTA in combination with ion exchange chromatography were explored in order to achieve such a separation. Due to the advanced rubidium separation ability of the developed DCTA elution method, it has been employed in all wine and soil sample preparations. Since chromatographic ion exchange procedures are not capable of removing all the rubidium from the sample matrices, 87Sr/86Sr ratio values were mathematically corrected for residual rubidium using an 88Sr correction. Since strontium isotope ratio measurements require very good precision, it is traditionally determined using TIMS. However, due to the ease of operation, shorter analysis time and widespread availability of quadrupole ICP-MS, the technique was evaluated for its merit for determining strontium isotope ratios. The optimization of acquisition parameters for the determination of the 87Sr/86Sr ratio in wine and soil samples with good precision of below 0.1% RSD has been conducted. Furthermore, selected sample matrix components were assessed as possible matrix interferences as well as for their ability to affect the precision of measurements. It was concluded that with adequate optimization of acquisition parameters, proper sample preparation and reliable mathematical correction of data, 87Sr/86Sr ratio measurements with reasonable precision could be obtained using quadrupole ICP-MS.