Multicollector Inductively Coupled Mass Spectrometer Research Articles

Precise Determination of the Lutetium Isotopic Composition in Rocks and Minerals Using Multicollector ICPMS

Evidence of (176)Hf excess in select meteorites older than 4556Ma was suggested to be caused by excitation of long-lived natural radionuclide (176)Lu to its short-lived isomer (176m)Lu, due to an irradiation event during accretion in the early solar system. A result of this process would be a deficit in (176)Lu in irradiated samples by between 1‰ and 7‰. Previous measurements of the Lu isotope ratio in rock samples have not been of sufficient precision to resolve such a phenomenon. We present a new analytical technique designed to measure the (176)Lu/(175)Lu isotope ratio in rock samples to a precision of ~0.1‰ using a multicollector inductively coupled mass spectrometer (MC-ICPMS). To account for mass bias we normalized all unknowns to Ames Lu. To correct for any drift and instability associated with mass bias, all standards and samples are doped with W metal and normalized to the nominal W isotopic composition. Any instability in the mass bias is then corrected by characterizing the relationship between the fractionation factor of Lu and W, which is calculated at the start of every analytical session. After correction for isobaric interferences, in particular (176)Yb, we were able to measure (176)Lu/(175)Lu ratios in samples to a precision of ~0.1‰. However, these terrestrial standards were fractionated from Ames Lu by an average of 1.22 ± 0.09‰. This offset in (176)Lu/(175)Lu is probably caused by isotopic fractionation of Lu during industrial processing of the Ames Lu standard. To allow more straightforward data comparison we propose the use of NIST3130a as a bracketing standard in future studies. Relative to NIST3130a, the terrestrial standards have a final weighted mean δ(176)Lu value of 0.11 ± 0.09‰. All samples have uncertainties of better than 0.11‰; hence, our technique is fully capable of resolving any differences in δ(176)Lu of greater than 1‰.

Isotopic characterisation of in-house purified progesterone for 13C/12C isotope ratios by multicollector ICP-MS

In this paper, a multicollector inductively coupled mass spectrometer (MC-ICP-MS) has been used for the first time to characterise a steroid sample for carbon isotope ratio traceable to SI. The progesterone sample was purified in house using semi-preparative high performance liquid chromatography (HPLC) and characterised using a multi-method approach. Carbon 13C/12C isotope amount ratios have been measured for the progesterone standard and NIST RM materials have been used as QCs to test instrumental performance and linearity over the δ13C range from −46 to +37‰. Internal normalisation by measuring boron 11B/10B isotope amount ratios has been used to correct for the effects of instrumental mass bias. Absolute 13C/12C ratios have been measured and corrected for instrumental mass bias and full uncertainty budgets have been calculated using the Kragten approach. Alternatively raw ratios have been measured for four isotopic NIST RMs and used for external calibration. This work proves the suitability of the method for the measurement of carbon isotope ratios within the natural range of variation of organic carbon compounds. The potential of the method for the production of isotopic reference standards to be used in metabolic studies, sports science and forensic testing is shown. Measured/corrected value for carbon isotope ratios traceable to the SI for the compound of interest and its combined uncertainty budget (including instrumental error and each parameter contributing to Russell expression for mass bias correction) were found to be 0.010853 ± 0.000011. The main advantages of the method versus conventional Isotope Ratio Mass Spectrometry (IRMS) measurements are that the carbon isotope ratios are measured as C+ instead of CO2+ and therefore an oxygen correction is not required. Moreover, absolute carbon isotope ratios can be measured and expressed as 13C/12C instead of δ13C (relative differences in ‰ between a reference standard and the sample).

Precise and Traceable 13C/12C Isotope Amount Ratios by Multicollector ICPMS

A new method for the measurement of SI traceable carbon isotope amount ratios using a multicollector inductively coupled mass spectrometer (MC-ICPMS) is reported for the first time. Carbon (13)C/(12)C isotope amount ratios have been measured for four reference materials with carbon isotope amount ratios ranging from 0.010659 (delta(13)C(VPDB) = -46.6 per thousand) to 0.011601 (delta(13)C(VPDB) = +37 per thousand). Internal normalization by measuring boron (11)B/(10)B isotope amount ratios has been used to correct for the effects of instrumental mass bias. Absolute (13)C/(12)C ratios have been measured and corrected for instrumental mass bias and full uncertainty budgets have been calculated using the Kragten approach. Corrected (13)C/(12)C ratios for NIST RM8545 (Lithium Carbonate LSVEC), NIST RM8573 (L-Glutamic Acid USGS40), NIST RM8542 (IAEA-CH6 Sucrose) and NIST RM8574 (L-Glutamic Acid USGS41) differed from reference values by 0.06-0.20%. Excellent linear correlation (R = 0.9997) was obtained between corrected carbon isotope amount ratios and expected carbon isotope amount ratios of the four chosen NIST RMs. The method has proved to be linear within this range (from (13)C/(12)C = 0.010659 to (13)C/(12)C =0.011601), and therefore, it is suitable for the measurement of carbon isotope amount ratios within the natural range of variation of organic carbon compounds, carbonates, elemental carbon, carbon monoxide, and carbon dioxide. In addition, a CO2 gas sample previously characterized in-house by conventional dual inlet isotope ratio mass spectrometry has been analyzed and excellent agreement has been found between the carbon isotope amount ratio value measured by MC-ICPMS and the IRMS measurements. Absolute values for carbon isotope amount ratios traceable to the SI are given for each NIST RM, and the combined uncertainty budget (including instrumental error and each parameter contributing to Russell expression for mass bias correction) has been found to be < 0.1% for the four materials. The advantage of the method versus conventional gas source isotope ratio mass spectrometry measurements is that carbon isotope amount ratios are measured as C(+) instead of CO2(+), and therefore, an oxygen (17)O correction due to the presence of (12)C(17)O(16)O(+) is not required. Organic compounds in solution can be measured without previous derivatization, combustion steps, or both, thus making the process simple. The novel methodology opens new avenues for the measurement of absolute carbon isotope amount ratios in a wide range of samples.

High Precision Measurements of Non-Mass-Dependent Effects in Nickel Isotopes in Meteoritic Metal via Multicollector ICPMS

We measured the Ni isotopic composition of metal from a variety of meteorite groups to search for variations in the 60Ni abundance from the decay of the short-lived nuclide 60Fe (t(1/2) = 1.49 My) and for possible nucleosynthetic effects in the other stable isotopes of Ni. We developed a high-yield Ni separation procedure based on a combination of anion and cation exchange chromatography. Nickel isotopes were measured on a single-focusing, multicollector, inductively coupled mass spectrometer (MC-ICPMS). The external precision on the mass-bias-corrected 60Ni/58Ni ratio (+/-0.15 epsilon; 2sigma) is comparable to similar studies using double-focusing MC-ICPMS. We report the first high-precision data for 64Ni, the least abundant Ni isotope, obtained via MC-ICPMS. The external precision on the mass-bias-corrected 64Ni/58Ni ratio (+/-1.5 epsilon; 2sigma) is better than previous studies using thermal ionization mass spectrometry. No resolvable excesses relative to a terrestrial standard in the mass-bias-corrected 60Ni/58Ni ratio were detected in any meteoritic metal samples. However, resolvable deficits in this ratio were measured in the metal from several unequilibrated chondrites, implying a 60Fe/56Fe ratio of approximately 1 x 10(-6) at the time of Fe/Ni fractionation in chondritic metal. A 60Fe/56Fe ratio of (4.6 +/- 3.3) x 10(-7) is inferred at the time of Fe/Ni fractionation on the parent bodies of magmatic iron meteorites and pallasites. No clearly resolvable non-mass-dependent anomalies were detected in the other stable isotopes of Ni in the samples investigated here, indicating that the Ni isotopic composition in the early solar system was homogeneous (at least at the level of precision reported here) at the time of meteoritic metal formation.