ISOprint - Analytical tools for the determination of isotopi

ISOprint - Development of Diffusive Gradient in Thin Films (DGT) multi-collector ICP-MS techniques for location-specific isotopic fingerprinting of S, Sr and Pb in soils as a tool for the provenance determination of primary agricultural products The aim of this project is to develop a technique for sampling the biologically available (bioavailable) fraction of sulfur (S), strontium (Sr) and lead (Pb) from soils. Subsequently, the isotopic composition of these elements will analyzed. The motivation behind is that a site-specific variation of isotopic composition of S, Sr and Pb in soil can act as specific fingerprint. This fingerprint is mirrored in plants growing on this soil. The isotopic difference can be caused by variations in the geology, by natural processes (e.g. microbial activities) or by anthropogenic activities (e.g. by combustion of fossil fuels containing S or petrol containing Pb). Diffusive gradients in thin films (DGT) represent an efficient passive sampling technique. DGT takes up elements from soil in the same way plants do, simply by diffusion. In this (bioavailable) fraction, the isotopic composition of the investigated elements will be analyzed by a dedicated mass spectrometer. Within this project, we want to develop a novel technique, which enables to take up S, Sr and Pb from soil without causing any change in the isotopic composition of these elements. takes up the part of S, Sr and Pb, which would be taken up by plants (bioavailable fraction) and the isotopic composition of these elements taken up by DGT from soil equals to that of plants grown on the same soil. allows for the establishment of a direct link of the chemical information stored in soils to the information found in primary agricultural products and therefore allows for provenancing. For the first time, the bioavailable chemical isotopic information is assessed directly. Within this project, new binding layers for S and Sr will be developed making use of the expertise of the collaborating company, which provides an expertise on novel resin materials. The results of this findings will be compared to greenhouse and field experiments. The goal of this approach is that we will be able to determine the site-specific isotopic signal and use it to investigate the origin of agricultural products by comparing their isotopic composition with the bioavailable fraction found in soil.

The analytical method developments accomplished within the ISOprint project enabled the targeted analysis of the elemental content and isotopic composition of sulfur (S), strontium (Sr), and lead (Pb) in biologically available (bioavailable) fractions of soils. Variations in the isotopic composition of these elements in bioavailable soil fractions can act as a site-specific isotopic fingerprint (signature) which is mirrored in plants grown on this soil. Therefore, bioavailable S, Sr, and Pb isotopic signatures are successfully applied as tracers in studies on food provenance and authenticity. However, so far, the bioavailable fractions of elements in soil were usually determined using chemical extractions, which do not mimic element uptake by plants and produce sample matrices that hamper isotope ratio analysis by mass spectrometry. Targeted sampling using the diffusive gradients in thin films (DGT) technique can overcome these issues, as it provides a mechanistic surrogate for elemental bioavailability and allows for matrix separation and analyte preconcentration already during sampling. In this project, new DGT techniques capable of quantitative S, Sr, and Pb sampling from soil were developed and fully validated. The techniques did not cause any significant change in the isotopic composition of these elements, enabling the accurate assessment of the site-specific bioavailable isotopic information. Moreover, the DGT technique was successfully extended for the simultaneous assessment of Sr and Pb concentrations and isotope ratios from the same sample within a single sampling step, which has not been possible before. The comprehensive assessment of the isotopic composition of bioavailable S, Sr, and Pb in a range of soils demonstrated the unique capability of the developed methods for robust soil discrimination according to the geographic location. Greenhouse and field experiments showed that the site- specific isotopic signature of Sr and Pb assessed by DGT from soil equals to that of plants grown on the same soil, confirming the applicability of the method for food provenancing. In addition, several project-related collaborations in the field of DGT-based chemical imaging were accomplished, providing a scientific basis to visualize and quantify bioavailable isotope signatures at high spatial resolution. The innovative methods gained in this project are versatile tools for environmental analysis and source tracing of S, Sr, and Pb, which open new analytical capabilities for the provenance determination of primary agricultural products and can be further extended to other disciplines such as archeology, (food) forensics, (eco)geochemistry, and environmental science.