Precise Analysis of Gallium Isotopic Composition by MC-ICP-MS

Abstract

Though an isotope approach could be beneficial for better understanding the biogeochemical cycle of gallium (Ga), an analogue of the monoisotopic element aluminum (Al), the geochemistry of Ga isotopes has not been widely elaborated. We developed a two-step method for purifying Ga from geological (biological) samples for precise measurement of Ga isotope ratio using multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS). Ga was thoroughly separated from other matrix elements using two chromatographic columns loaded with AG 1-X4 and Ln-spec resin, respectively. The separation method was carefully calibrated using both synthetic and natural samples and validated by assessing the extraction yield (99.8 ± 0.8%, 2SD, n = 23) and the reproducibility (2SD uncertainty better than 0.05‰, n = 116) of the measured isotopic ratio (expressed as δGa). The validation of the whole protocol, together with instrumental analysis, was confirmed by the investigation of the matrix effect, the result of a standard addition experiment, and the comparison of Ga isotope measurement on two mass spectrometers-Nu Plasma II and Neptune Plus. Although the measurements using the sample-standard bracketing (SSB) correction method on both instruments resulted in identical δGa values for reference materials, the modified empirical external normalization (MEEN) method gave relatively better precision compared to SSB on Neptune. Our preliminary results showed large variation of δGa (up to 1.83‰) for 10 standards, with higher values in industrially produced materials, implying potential application of Ga isotopes.

Accurate Measurement of Lithium Isotopes in Eleven Carbonate Reference Materials by MC‐ICP‐MS with Soft Extraction Mode and 1012 Ω Resistor High‐Gain Faraday Amplifiers

“…, Yuan et al . ). Taking GSR‐6 (the residual Na and Ca content is relatively high) as an example, the standard addition method experiment was carried out by mixing the L‐SVEC and GSR‐6 solutions with GSR‐6 proportions of 100%, 80%, 60%, 40%, 20% and 0% (Table ).…”

Determination of Gallium Isotopic Compositions in Reference Materials

“…Anionic exchange chromatography is widely used for the purification of Pb (Manhes et al ), Cu, Zn (Maréchal et al , Moynier and Le Borgne ), Fe (Zhu et al ), Cd (Schmitt et al ), Zr (Inglis et al ), Ti (Deng et al ) and Mo (Pearce et al ). Gallium exhibits similar adsorption behaviour to Fe on anionic exchange resin (Machlan and Gramlich , Yuan et al , Zhang et al , Kato et al ). Most cations are not retained on anionic exchange resin under a continuous high concentration hydrochloric acid medium, but Fe and Ga are highly absorbed.…”

“…A number of tests have been conducted to ascertain the influence of the sample matrix on the precise determination of Ga isotopic compositions in previous studies (Yuan et al , Zhang et al , Kato et al ). Briefly, the δ 71 Ga values were found to be sensitive to Ba and Ce contents in the sample solutions because 138 Ba 2+ and 138 Ce 2+ , and 142 Ce 2+ can induce interferences on 69 Ga + and 71 Ga + , respectively (Yuan et al , Kato et al ) . Kato et al () reported that when [Ba]/[Ga] and [Ce]/[Ga] ratios reached 2 × 10 −5 and 4 × 10 −3 , respectively, a significant offset of δ 71 Ga was observed (> 0.07‰).…”

“…On the other hand, although δ 71 Ga values are not as susceptible to other elements as to Ba and Ce, matrix elements can still produce noticeable effects on the precision and accuracy of Ga isotope determinations. For example, significant drifts in δ 71 Ga were observed when [Fe]/[Ga] > 5 (Zhang et al ) and [Zn]/[Ga] > 0.1 (Yuan et al ) applied in sample solutions . No observable δ 71 Ga ratio shift was detected over the measured range for the other elements when [Cu]/[Ga] ≤ 0.25, [Mo]/[Ga] ≤ 1.2 and [Ge]/[Ga] ≤ 5 were applied (Yuan et al , Zhang et al ).…”

“…The recent advent of multi‐collector inductively coupled plasma‐mass spectrometry (MC‐ICP‐MS) has generated increasing interest in isotope fractionation studies of stable isotope systems, such as Fe (Zhu et al ), Cu, Zn (Maréchal et al ), Ca (Heuser et al ) and Mg (Galy et al ). High precision Ga isotope measurement methods by MC‐ICP‐MS have been established in the past 3 years, allowing the distinction of small Ga isotopic variations (0.04‰, 2 s level) in geological materials (Yuan et al , Zhang et al , Kato et al ). Consequently, significant Ga isotopic fractionation was observed during volatile depletion events on planets (Kato and Moynier , Kato and Moynier ) and solid–fluid interactions (Yuan et al ), indicating that the Ga isotope ratio can be a powerful tracer for the study of the early history of the solar system and biogeochemical processes at the Earth's surface.…”