Isotope Dilution-Total Evaporation-Thermal Ionization Mass Spectrometric Direct Determination of Radioactive Strontium-90 in Microdrop Samples

Advances in mass spectrometry for metabolomics: Strategies, challenges, and innovations in disease biomarker discovery

Mass spectrometry (MS) plays a crucial role in metabolomics, especially in the discovery of disease biomarkers. This review outlines strategies for identifying metabolites, emphasizing precise and detailed use of MS techniques. It explores various methods for quantification, discusses challenges encountered, and examines recent breakthroughs in biomarker discovery. In the field of diagnostics, MS has revolutionized approaches by enabling a deeper understanding of tissue-specific metabolic changes associated with disease. The reliability of results is ensured through robust experimental design and stringent system suitability criteria. In the past, data quality, standardization, and reproducibility were often overlooked despite their significant impact on MS-based metabolomics. Progress in this field heavily depends on continuous training and education. The review also highlights the emergence of innovative MS technologies and methodologies. MS has the potential to transform our understanding of metabolic landscapes, which is crucial for disease biomarker discovery. This article serves as an invaluable resource for researchers in metabolomics, presenting fresh perspectives and advancements that propels the field forward.

Direct Quantification of Attogram Levels of Strontium-90 in Microscale Biosamples Using Isotope Dilution-Thermal Ionization Mass Spectrometry Assisted by Quadrupole Energy Filtering

Although thermal ionization mass spectrometry (TIMS) has been employed for the high-precision analysis of isotope ratios, direct quantification of artificial mono-nuclide in the environment is difficult by even using isotope dilution (ID) due to the coexistence of the great magnitude of natural stable nuclides or isobars. In traditional TIMS and ID-TIMS, a sufficient amount of stable Sr doped on a filament is required to realize a stable and adequate ion-beam intensity (i.e., thermally ionized beams). However, the background noise (BGN) at m/z 90, detected by an electron multiplier, disturbs ⁹⁰Sr analysis at low concentration levels due to peak tailing of a significant ⁸⁸Sr ion beam dependent on the ⁸⁸Sr-doping amount. Here, TIMS assisted by quadruple energy filtering was successfully employed for the direct quantification of attogram levels of an artificial monoisotopic radionuclide strontium-90 (⁹⁰Sr) in microscale biosamples. Direct quantification was achieved by integrating the ID quantification of natural Sr and simultaneous ⁹⁰Sr/⁸⁶Sr isotope ratio analysis. Additionally, the measurement amount calculated by the combination of the ID and intercalibration was corrected for the net result amount of ⁹⁰Sr by subtracting dark noise and the detected amount derived from the survived ⁸⁸Sr, which are equivalent with the BGN intensity at m/z 90. Background correction revealed that the detection limits were in the range of 6.15 × 10^-2-3.90 × 10^-1 ag (0.31-1.95 μBq), depending on the concentration of natural Sr in a 1 μL sample, and the quantification of 0.98 ag (5.0 μBq) of ⁹⁰Sr in 0-300 mg/L of natural Sr was successful. This method could analyze small sample quantities (1 μL), and the quantitative results were verified against authorized radiometric analysis techniques. Furthermore, the amount of ⁹⁰Sr in actual teeth was successfully quantified. This method will be a powerful tool for measuring ⁹⁰Sr in the measurement of micro-samples, which are required to assess and understand the degree of internal radiation exposure.

Novel 90Sr analysis of environmental samples by Ion-Laser InterAction Mass Spectrometry

The sensitive analysis of ⁹⁰Sr with accelerator mass spectrometry (AMS) was developed to advance environmental radiology. One advantage of AMS is the ability to analyze environmental samples with ⁹⁰Sr/⁸⁸Sr atomic ratios of 10^-14 in following a simple chemical separation. Three different IAEA samples with known ⁹⁰Sr concentrations (moss-soil, animal bone, Syrian soil: 1 g each) were analyzed to assess the validity of the chemical separation and the AMS measurement. The ⁹⁰Sr measurements were conducted on the AMS system VERA combined with the Ion Laser InterAction Mass Spectrometry (ILIAMS) setup at the University of Vienna, which has excellent isobaric separation performance. The isobaric interference of ⁹⁰Zr in the ⁹⁰Sr AMS was first largely removed by chemical separation. The separation factor of Zr in two-step column chromatography with Sr resin and anion exchange resin was 10⁶. The ⁹⁰Zr remaining in the sample was effectively suppressed by ILIAMS. This procedure achieved a limit of detection <0.1 mBq in the ⁹⁰Sr AMS, which is lower than typical β-ray detection. The agreement between AMS measurements and nominal values for the ⁹⁰Sr concentrations of IAEA samples indicated that the new highly-sensitive ⁹⁰Sr analysis in the environmental samples with AMS is reliable.

Online solid-phase extraction-inductively coupled plasma-quadrupole mass spectrometric quantification of 90Sr using 88Sr/86Sr isotope dilution method

Due to the lack of a correlation with the natural Strontium (Sr) isotopes, it is difficult to apply the isotope dilution (ID) method to an artificial radioactive mononuclide Strontium-90 (⁹⁰Sr), in inductively coupled plasma-quadrupole mass spectrometry (ICP-QMS). Meanwhile, online solid-phase extraction (SPE)-ICP-QMS (SPE-ICP-QMS) serves as an automatic sequential analytical technique for measuring the ultra-trace amounts of radionuclides; however, apparent assay values obtained using this method are often negatively affected by differences in the sample matrix composition between standard and actual samples. In this study, the pg L^-1 level of ⁹⁰Sr was successfully measured by combining online SPE-ICP-QMS and the ID method with ⁸⁸Sr/⁸⁶Sr ratios in one sample injection, without the radioactive standard. Although naturally occurring abundant isobaric ⁹⁰Zr significantly influences ⁹⁰Sr quantification during mass spectrometry, consecutive separations between automated SPE and dynamic reaction cell (DRC) oxidation enable ⁹⁰Sr quantification, even in the presence of isobaric ⁹⁰Zr (acceptable down to 5.7 × 10^-9 of ⁹⁰Sr/Zr in sample solution), using this method. Through this method, both radioactive ⁹⁰Sr and naturally occurring Sr were simultaneously quantified using ⁸⁸Sr-to-⁸⁶Sr and ⁸⁸Sr-to-⁹⁰Sr ratios without radioactive ⁹⁰Sr standard solutions. This simultaneous quantification of stable Sr and ⁹⁰Sr was achieved within 15 min with good recovery rates. The limit of detection of ⁹⁰Sr was 1.1 pg L^-1 (equivalent to radioactivity 5.6 Bq L^-1) for a 10 mL injection. Finally, water collected from an actual contaminated water storage tank at the Fukushima Daiichi Nuclear Power Plant (Fukushima, Japan) was analyzed using the proposed method, and the obtained results agreed well with those obtained using conventional analytical methods.

A part per trillion isotope ratio analysis of 90Sr/88Sr using energy-filtered thermal ionization mass spectrometry

Strontium-90 is a major radioactive nuclide released by nuclear accidents and discharge waste. Input of such radioactive nuclide into earth surface environment causes potential threat of long-term internal exposure when taken up by organism. Rapid and precise measurement of ⁹⁰Sr in variety of environmental sample is important to understand the distribution and dynamics of ⁹⁰Sr in the local environment after the accident and to assess the effect of radioactive nuclide inputs on bodies. However, previous ⁹⁰Sr measurement techniques have drawbacks such as long measurement times for radiometry and high detection limits for mass spectrometry. Here we present a technique to accurately measure a significantly small amount of ⁹⁰Sr in natural environmental samples using an energy-filtered thermal ionization mass spectrometry. Our technique achieved a ⁹⁰Sr detection limit of 0.23 ag, which corresponds to a ⁹⁰Sr activity of 1.2 µBq. The detection limit was lowered by two orders of magnitude compared with the previous mass spectrometric ⁹⁰Sr analyses. The ability of our technique will expand the applicability of mass spectrometric ⁹⁰Sr survey not only to the rapid ⁹⁰Sr survey upon nuclear accidents but also to study a long-term environmental diffusion of radioactive materials using size-limited environmental and biological samples.

Ion-imprinted resin for use in an automated solid phase extraction system for determining 90Sr in environmental and human samples

In 90Sr analysis, determining its daughter 90Y improves the sensitivity of the radiometric methods. We found that to imprint a cavity made of [Y(6-(4-Vinylphenylcarbamoyl)pyridine-2-carboxylate)3] into a polystyrene skeleton yields a solid phase extraction resin with high selectivity for Y and Ln(III) over transition metals, alkaline, and alkaline-earth cations. We used this resin in an automated chromatography system to extract 90Y from milk, grass, vegetables, soil, sediments, water, human bones, and milk teeth samples. We found that the ion-imprinted resin could be used to separate light Ln(III) using a pH gradient, favoring the targeting of molecules used in nuclear medicine.