A practical guide for the design and implementation of the double-spike technique for precise determination of molybdenum isotope compositions of environmental samples

• Published in: Analytical and bioanalytical chemistry 2015-03, Vol.407 (7), p.1925-1935
• Main Authors: Skierszkan, E. K., Amini, M., Weis, D.
• Format: Article
• Language: English
• Subjects: Accuracy; Analytical Chemistry; Atmospheric sciences; Biochemistry; Calibration; Characterization and Evaluation of Materials; Chemical analysis; Chemical properties; Chemistry; Chemistry and Materials Science; Environmental aspects; Environmental monitoring; Food Science; Fractionation; Geological surveys; Identification and classification; Isotope ratios; Isotopes; Laboratories; Laboratory Medicine; Mass spectrometry; Mathematical analysis; Methods; Molybdenum; Molybdenum isotopes; Monitoring/Environmental Analysis; Ratios; Reference materials; Reproducibility; Research Paper; Scientific imaging; Seawater; Spectrometry; Stable isotopes; Water analysis
• ISSN: 1618-2642; 1618-2650
• DOI: 10.1007/s00216-014-8448-6

The isotopic double-spike method allows for the determination of stable isotope ratios by multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS) with accuracy and precision in the range of ∼0.02 ‰ amu −1 , but its adoption has been hindered by the perceived difficulties in double-spike calibration and implementation. To facilitate the implementation of the double-spike approach, an explanation of the calibration and validation of a 97 Mo- 100 Mo double-spike protocol is given in more detail than has been presented elsewhere. The long-term external standard reproducibility is 0.05 ‰ on δ 98/95 Mo measurements of standards. δ 98/95 Mo values for seawater and U.S. Geological Survey (USGS) reference materials SDO-1 and BCR-2 measured in this study are 2.13 ± 0.04 ‰ (2 SD, n  = 3), 0.79 ± 0.05 ‰ (2 SD, n  = 11), and −0.04 ± 0.10 ‰ (2 SD, n  = 3) relative to the NIST-SRM-3134. The double-spike method corrects for laboratory and instrumental fractionation which are not accounted for using other mass bias correction methods. Spike/sample molar ratios between 0.4 and 0.8 provide accurate isotope measurements; outside of this range, isotope measurements are inaccurate but corrections are possible when standards and samples are spiked at a similar ratio.