The Thermal Ionization Mass Spectrometry (TIMS) Laboratory routinely performs analyses of Sr, Nd and Os radiogenic isotopes and also conducts research focusing primarily on the origin of igneous rocks. It also deals with isotope studies involving many broader interdisciplinary projects (archaeology, environmental geochemistry). Samples for the majority of analyses are prepared in a specialized Ultratrace Laboratory (USL) with controlled sterility. The preparation of Os samples is carried out in cooperation with the Institute of Geology of the Czech Academy of Sciences.
The laboratory provides services mainly to internal staff members, but smaller contracts may also be arranged for individuals as well as the cooperation with science and education departments. Selected isotope analyses can also be performed as commercial contracts. All contracts must be consulted in advance with the laboratory staff.
Range of Services
- Routine determination of the isotopic composition of Sr, Nd and Os using a TIMS instrument (analysis details are specified in the Price list)
Equipment
- Thermo Fisher Scientific Triton Plus solid-source thermal ionization mass spectrometer
Analysis Procedure
Samples are prepared in the Ultratrace Laboratory (USL), which is a pressurized cleanroom with controlled air cleanliness (ISO 7, corresponding to cleanroom class 10,000) and controlled temperature and humidity, where the necessary sample preparation (mineralization, separation of studied elements from the matrix) is carried out in order to determine isotopic ratios using mass spectrometry (TIMS, MC ICP-MS).
Chromatographic separation is performed prior to the actual isotopic composition analysis to separate the analyte element from the other elements in the sample (matrix). The reason for this is to achieve a coherent ion beam and subsequent easier detection of ions and, above all, to avoid isobaric interferences during the measurement. The most common method of separating chemical elements for isotopic analysis is ion-exchange chromatography. The principle of chemical separation on ion exchangers is to establish a reversible equilibrium between the stationary phase and mobile phase. The stationary phase usually is the actual ion exchanger with an acidic or basic functional group on an inert support medium. The separation is performed in a glass, quartz or plastic column packed with the stationary phase (ion exchanger), through which the mobile phase (dissolved sample) flows. Separation techniques on ion exchangers vary based on the size of the separated sample, the matrix composition, the amount of ion exchanger used, and on the size (volume) of the separation columns. Since isotopic fractionation may occur during sample separation, an overall separation yield of nearly 100 % is a prerequisite for an effective separation.
The mass spectrometer (TIMS, MC ICP-MS) comrizes three parts – an ion source, an analyzer and a detector. The ion source in TIMS instruments is an electrically heated metallic filament (ribbon) on which a solid-phase sample (a vaporized droplet) is deposited. By selecting a suitable filament material (Re, Ta, Pt, W), elements with relatively lower ionization energy are ionized when the filament is heated.
An accelerating voltage of approximately 10 kV is used to accelerate ions through a series of electromagnetic lenses towards the magnetic analyzer, which is a 90° static magnetic sector field with a radius of 23 cm. Passing through the magnetic field, the ions are separated by mass because the path of heavier ions logically curves less than that of lighter ions.
Faraday cup detectors, whose position may optimally be adjusted for a given isotope system, are used to measure the relative intensity of individual ion beams. A secondary electron multiplier is available for beams with very weak intensity.
Sample Requirements
A minimum of 1 g of analytical grade powder is usually required in the case of submitted rock samples for Sr and Nd isotope analysis and 100 ml in the case of water samples for Sr analysis. Samples of soluble carbonate rocks as well as tooth samples for enamel analysis may be submitted in pieces. The minimum total amount of Sr and Nd per sample is 2 μg and 200 ng, respectively, which should be taken into account for samples with very low concentrations and in cases where only a limited amount of material is available.
The sample documentation must include information on Sr and Nd concentrations, the exact material type (rock classification, water type) and locality.
Due to limited capacity, all requests should be consulted in advance with the laboratory staff.
The quality and applicability of the results of the laboratory analysis of natural material generally depends on several parameters, which must be taken into account during sampling:
- Sample representativeness – the sample composition must truly reflect the composition of a studied reservoir, which in the case of rock samples means, for instance, sufficient sample size with regard to grain size, absence of weathered products and so forth, and sample quartering during the preparation process.
- Sample purity – in many cases, the concentration of the element of interest in a sample is very low, and contamination may produce a significant shift in the isotope ratio value. Problems may arise particularly in situations where a contaminant has a contrasting isotopic composition or a high concentration of the element relative to the sample. The required analysis accuracy is a also factor.
- Sample material – in specific cases, analysis may be impeded by a difficult-to-dissolve sample. As a result, high concentrations of some elements may hinder the sample separation or measurement. The laboratory staff should be consulted in such cases.
