Effects of cone combinations on accurate and precise Mg‐isotopic determination using multi‐collector inductively coupled plasma mass spectrometry

Abstract

Rationale High‐precision determination of magnesium (Mg) isotopes can now be routinely achieved by multi‐collector inductively coupled plasma mass spectrometry (MC‐ICP‐MS). The analytical sensitivity and instrumental mass discrimination behavior of this method are, however, sensitive to the types of sample and skimmer cones used in these measurements, so it is important that these parameters should be investigated. Methods Using the sample‐standard‐bracketing method in the wet‐plasma mode, four available combinations of sample and skimmer cones [Jet sample cone + H skimmer cone (Jet + H), standard sample cone + H skimmer cone (Standard + H), standard sample cone + X skimmer cone (Standard + X), and Jet sample cone + X skimmer cone (Jet + X)] were systematically investigated for peak shape, sensitivity, mass discrimination, accuracy, and precision in Mg‐isotopic ratio determination using a Neptune plus MC‐ICP mass spectrometer. Results The results showed that different cone combinations do not affect peak shapes but would significantly change the sensitivities for Mg‐isotopic determinations. Compared with using the Standard + H, the sensitivities of Mg‐isotopic determinations were enhanced by approximately a factor of 1.3, 1.4, and 1.9 by using the Standard + X, the Jet + H, and the Jet + X combinations, with the most stable mass discrimination behaviors obtained by the Jet + H. The instrumental mass fractionation slope for any combination of a modified cone geometry (i.e. Standard + X, Jet + X, and Jet + H) is 0.500, while it is 0.510 for the Standard + H. In addition, the mass discrimination behavior is related to Mg concentrations once the combination is set, indicating the necessity of concentration match during Mg‐isotopic determination. Conclusions The precision and accuracy of the Jet + H combination are better than those of the other combinations, and this is further supported by the validation of the Mg‐isotope data for four international reference materials: Cambridge‐1, NASS‐6, AGV‐2, and BHVO‐2. As the Jet + H combination also provides a high signal, this combination gives the most robust strategy for the highly precise and accurate determination of Mg isotopes.

Magnesium Isotope Fractionation during Synthesis of Chlorophyll a and Bacteriochlorophyll a of Benthic Phototrophs in Hypersaline Environments

“…The δ 26 Mg values of the seawater reference materials NASS-6 and IAPSO Standard Seawater were −0.93 and −0.87‰ with 2σ reproducibility of 0.13 and 0.04‰, respectively. These values also agrees well with reported values for the same standards, −0.83 ± 0.07‰ (2σ) for NASS-6 and −0.87 ± 0.08‰ (2σ) for IAPSO Standard Seawater …”

Multicollector Inductively Coupled Plasma–Mass Spectrometry with 1013 Ω Faraday Cup Amplifiers for Ultrasensitive Mg Isotopic Analysis of Cerebrospinal Fluid Microsamples

“…15 Gou et al determined that the minimum Mg concentration should be >50 μg L −1 for obtaining accurate and precise Mg isotope ratios using an MC-ICP-MS unit equipped with a Jet interface and operated in a low mass resolution mode, otherwise the figures of merit are influenced by the background. 15 However, the use of (pseudo) medium mass resolution is recommended to resolve spectral interference originating from polyatomic ions, consisting of carbon, hydrogen, and/or nitrogen (e.g., C 2 + , C 2 H + , C 2 H 2 + , and CN + ), otherwise hampering Mg isotope ratio measurements when using a conventional sample introduction system. 16 The recent introduction of Faraday cup amplifiers with a high-gain 10 13 Ω resistor has been shown to be advantageous for high-precision isotopic analysis of Li, Ta, Re, and Pb by MC-ICP-MS and of Nd and U by thermal ionization mass spectrometry, 17−22 particularly for small size samples or lowabundance isotopes.…”

“…Magnesium isotope ratio measurements via multicollector inductively coupled plasma–mass spectrometry (MC-ICP-MS) are typically carried out by simultaneous monitoring of the ion signal intensities of the three stable isotopes 24 Mg, 25 Mg, and 26 Mg with relative isotopic abundances of 79, 10, and 11%, respectively. The concentrations at which Mg isotope ratio measurements are conducted using MC-ICP-MS typically range between 100 and 1000 μg L –1 , while low or (pseudo) medium mass resolution is used. , Some instrumental strategies can be used to decrease the concentration required for reliable Mg isotopic analysis via MC-ICP-MS; the use of a high-sensitivity Jet interface, for example, increases the Mg sensitivity by a factor of ∼2 . Gou et al determined that the minimum Mg concentration should be >50 μg L –1 for obtaining accurate and precise Mg isotope ratios using an MC-ICP-MS unit equipped with a Jet interface and operated in a low mass resolution mode, otherwise the figures of merit are influenced by the background .…”

“…The concentrations at which Mg isotope ratio measurements are conducted using MC-ICP-MS typically range between 100 and 1000 μg L –1 , while low or (pseudo) medium mass resolution is used. , Some instrumental strategies can be used to decrease the concentration required for reliable Mg isotopic analysis via MC-ICP-MS; the use of a high-sensitivity Jet interface, for example, increases the Mg sensitivity by a factor of ∼2 . Gou et al determined that the minimum Mg concentration should be >50 μg L –1 for obtaining accurate and precise Mg isotope ratios using an MC-ICP-MS unit equipped with a Jet interface and operated in a low mass resolution mode, otherwise the figures of merit are influenced by the background . However, the use of (pseudo) medium mass resolution is recommended to resolve spectral interference originating from polyatomic ions, consisting of carbon, hydrogen, and/or nitrogen (e.g., C 2 + , C 2 H + , C 2 H 2 + , and CN + ), otherwise hampering Mg isotope ratio measurements when using a conventional sample introduction system …”

Quantifying the impact of recovery during chromatographic purification on the accuracy of lithium isotopic determination by multi‐collector inductively coupled plasma mass spectrometry

“…Therefore, a standard‐sample‐bracketing method is the most common approach used to correct for instrumental mass discrimination and drift . The effect of matrix elements on accuracy can be identified using doping tests, and can then be avoided by monitoring matrix concentrations in purified aliquots . Fractionation caused by incomplete digestion of solid samples is avoidable when the solids are completely digested .…”