Interlaboratory comparison of magnesium isotopic compositions of 12 felsic to ultramafic igneous rock standards analyzed by MC‐ICPMS

Abstract

To evaluate the interlaboratory mass bias for high-precision stable Mg isotopic analysis of natural materials, a suite of silicate standards ranging in composition from felsic to ultramafic were analyzed in five laboratories by using three types of multicollector inductively coupled plasma mass spectrometer (MC-ICPMS). Magnesium isotopic compositions from all labs are in agreement for most rocks within quoted uncertainties but are significantly (up to 0.3& in 26 Mg/ 24 Mg, >4 times of uncertainties) different for some mafic samples. The interlaboratory mass bias does not correlate with matrix element/Mg ratios, and the mechanism for producing it is uncertain but very likely arises from column chemistry. Our results suggest that standards with different matrices are needed to calibrate the efficiency of column chemistry and caution should be taken when dealing with samples with complicated matrices. Well-calibrated standards with matrix elements matching samples should be used to reduce the interlaboratory mass bias.

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

“…The δ 26 Mg values of a seawater reference material (NASS‐6) and two rock reference materials (AGV‐2 and BHVO‐2) were also determined. The results (Table ) are in good agreement with the previous published values …”

“…However, the Jet + H combination has an instrumental mass fractionation slope that is distinct from that of the Standard + H. Further analyses aimed at measuring the Δ 25 Mg′ values of natural samples need to consider instrumental mass fractionation when using cones with modified geometry . For example, the cones used by Teng et al were different from one laboratory to another, leaving the possibility of difference between instrumental and sample mass fractionation factors resulting from cone geometry and natural sample matrix, which obviously needs further investigation.…”

“…Two in‐house standards (Cambridge‐1 and IGGCAS‐Mg) were analysed repeatedly for a one‐year period, and yielded δ 26 Mg = −2.603 ± 0.065‰ (2 s.d., n = 51) for the Cambridge‐1 standard and δ 26 Mg = −1.751 ± 0.070‰ (2 s.d., n = 53) for the IGGCAS‐Mg standard. These values agree well with the published data . The Δ 25 Mg’ results for Cambridge‐1 are also in agreement with literature data while IGGCAS‐Mg shows a slightly positive Δ 25 Mg’ value, which might result from the processes used in its purification .…”

Mg Isotope Interlaboratory Comparison of Reference Materials from Earth‐Surface Low‐Temperature Environments

“…(), other silicate rocks by Teng et al . (), IAPSO Atlantic seawater results by Foster et al . and carbonates by Pogge von Strandmann , Kasemann et al .…”

“…While δ 26 Mg and δ 25 Mg values of silicate rock RMs are available for high‐temperature systems (Teng et al . ), Mg isotope data of RMs representative of samples with complex matrices from Earth‐surface low‐temperature environments are scarce (Bolou‐Bi et al . , Foster et al .…”