Gallium (Ga) has special geochemical characteristics and important economic value, thus is of great interest in many research aspects. As the third element of the Group IIIA, Ga has chemical properties similar to the monoisotope element aluminum (Al), and is frequently used as a geochemical analog of Al. But unlike Al which is a major element, the trace element Ga sometimes behaves differently and the fractionation between Ga and Al (Ga/Al ratio) was usually used to investigate the transport and behaviors of trace elements in the ocean, rivers, and during weathering processes.

Ga is also involved in many biological processes and even enriched in some certain species. Ga has two stable isotopes (69 and 71) and the use of Ga isotopes may be useful for better understanding the biogeochemical of Ga. However, apart from several comparative studies on the abundance and distribution of Ga isotopes around the middle of last century, the geochemistry of Ga isotopes has not been widely elaborated up to now, due to probably the lack of an effective and reliable method. More research is thus required to better constrain the exact geochemical behaviors and the biogeochemical cycle of Ga.

Reproducibility of Ga isotope ratio (δ71Ga) for long-term measurements of the standard GBW(E) 08056 on the Nu Plasma II (A, red dots) and the Neptune Plus (B, blue rhombi) (Image by IGCAS)

The separation protocol was thoroughly calibrated and optimized using both synthetic and natural samples, and has been proven to be reproducible and satisfactory for precise Ga isotope ratio determination. The researchers found that the short-term analysis performed on both Nu and Neptune spectrometers gave identical δ71Ga values for natural materials, and a precision better than 0.05‰, comparable to that (0.05‰, 2SD, n = 116) of the long-term in-house standard calibration.

"Our preliminary results revealed large variation of δ71Ga (up to 1.83‰) in ten natural and industrial reference materials, stimulating further investigation of Ga isotopic composition in natural reservoirs and the relative fractionation mechanisms," said YUAN Wei, "We believe that this application of isotope approach would provide new insight into the study of the geochemistry cycle of Ga, for example, to distinguish the natural from anthropogenic sources of Ga. Meanwhile, the new isotopic system also provides a useful research tool for studies of cosmochemistry, crust-mantle differentiation, climatic changes and the surface weathering of the earth."

This work was financially supported by the Natural Science Foundation of China (U1301231, 41561134017) and the State Key Laboratory of Environmental Geochemistry, IGCAS (SKLEG2016001). The paper entitled “Precise analysis of Gallium isotopic composition by MC-ICP-MS” was published in Analytical Chemistry (2016, 88(19), pp 9606-9613).