Abstract
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.