IRMS and SIMS carbon and oxygen isotope measurement in carbonates (δ13C and δ18O)
Conventional isotope measurement techniques for carbon (δ13C) and oxygen (δ18O) are essential for understanding the geochemical history of carbonate rocks. δ13C and δ18O values can indicate paleoenvironmental conditions, including temperature, water composition, and diagenetic processes such as cementation and recrystallisation. By analysing the isotopic composition of different carbonate phases, geologists can distinguish between primary deposition and subsequent diagenetic alterations. For example, variations in δ13C and δ18O values can identify stages of early marine diagenesis, meteoric diagenesis, and burial diagenesis.
Instruments and IRMS Techniques
For δ13C and δ18O measurements, Isotope Ratio Mass Spectrometry (IRMS – Delta V) is employed. In this method, samples are converted to CO2 gas, typically through a reaction with phosphoric acid. The resulting CO2 gas is then analyzed in the mass spectrometer to determine the isotopic ratios.
Sample preparation and powder sampling
For carbon and oxygen isotope measurements by IRMS, approximately 1-2 mg of carbonate powder is required. The samples should be clean, free of contaminants, and representative of the mineral phase of interest to ensure accurate results. The measurement of carbonate oxygen and carbon isotopes can be done at different scales and using various sampling techniques. Here’s an overview of the main methods used:
Conventional IRMS on Powder Samples collected with a Dremel: Using a Dremel tool, samples are collected as powder from a 2 mm wide area. This method is useful for obtaining bulk measurements of isotopic ratios from a relatively large sample area. It is quick and easy to perform, making it suitable for homogenised or large-scale samples. However, it has less spatial resolution and may mix isotopic signals from different growth layers or phases within the sample.
Conventional IRMS on micro-powder sample collected with a Micro-mill System: The micro-mill system allows for targeted sampling of very small areas, ranging from sub-millimeter to millimeter scale. This method is ideal for extracting samples from specific microstructural features within a carbonate, such as growth layers or distinct mineral phases. It offers higher spatial resolution compared to macro-sampling, enabling detailed study of isotopic variations within a sample. Although it is more time-consuming and requires careful handling to avoid contamination, it provides a more precise analysis.
Precision and accuracy
Isotope Ratio Mass Spectrometry (IRMS) for carbon and oxygen isotopes can achieve a precision of ±0.1‰ for δ13C and ±0.2‰ for δ18O. These high levels of precision are essential for reliable isotopic measurements and subsequent geological interpretations.
Cost of δ13C and δ18O Analysis and delay
To provide accurate pricing and an official quote, please specify the number of samples along with the name and billing address of the paying institution. Normally, the turnaround time is in the order of two to four weeks, depending on the number of new samples submitted and those already on the waiting list.
An alternative approach – Ion microprobe for in-situ C/O isotope analyses in carbonate matrix
The ion microprobe, or Secondary Ion Mass Spectrometry (SIMS), enables direct analysis of the isotopic composition of carbonates at the microscopic scale without the need to extract a physical sample. This method is used for high-precision, in-situ measurements on thin or thick sections of rock, providing detailed isotopic mapping across small sample areas. It offers ultra-high spatial resolution, typically in the range of 1-10 micrometers, allowing for the study of fine-scale isotopic variations and microstructural features within individual crystals or zones. SIMS can measure isotopic ratios with an accuracy of better than ±1‰ for carbon and oxygen isotopes on carbonate. The primary advantage of SIMS is its ability to conduct high-resolution isotopic analyses directly on rock sections, making it ideal for studying isotopic variations within complex carbonate structures, such as growth layers, diagenetic features, or fine-scale mineral inclusions. However, the technique involves highly specialised and expensive equipment, requiring well-prepared samples and extensive expertise to operate. H-ES can offer this service—please contact us for more details, delays, and pricing (xavier.mangenot@h-expertise-services.com).
Comprehensive carbonate C/O analytical services offered by H-Expertise Service
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At H-Expertise Services, we leverage advanced techniques, state-of-the-art equipment, and the expertise of our geochemist with decades of practical experience to ensure you receive precise and insightful data, deepening your understanding of geological systems. Partner with us for unmatched expertise and impactful results. Please contact our specialist, Xavier Mangenot, at xavier.mangenot@h-expertise-services.com to discuss your operational needs, pricing, and to design a customised analytical strategy tailored to your requirements.
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