A Study on Memory Effects in Lithium and Boron Isotope Analysis Using MC-ICP-MS

TANG Qingyu; CHEN Lu; TIAN Shihong; HU Wenjie; GONG Yingli; ZI Yanmei

doi:10.15898/j.ykcs.202310260167

Rock and Mineral Analysis > 2024 > 43(2): 201-212. > DOI: 10.15898/j.ykcs.202310260167

TANG Qingyu，CHEN Lu，TIAN Shihong，et al. A Study on Memory Effects in Lithium and Boron Isotope Analysis Using MC-ICP-MS[J]. Rock and Mineral Analysis，2024，43（2）：201−212. DOI: 10.15898/j.ykcs.202310260167

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A Study on Memory Effects in Lithium and Boron Isotope Analysis Using MC-ICP-MS

TANG Qingyu^{1, 2,},
CHEN Lu^2, ,,
TIAN Shihong^{1, 2},
HU Wenjie²,
GONG Yingli³,
ZI Yanmei^{1, 2}

1.
School of Earth Sciences, East China University of Technology, Nanchang 330013, China
2.
State Key Laboratory of Nuclear Resources and Environment, East China University of Technology, Nanchang 330013, China
3.
Department of Energy and Power Engineering, Tsinghua University, Beijing 100084, China

More Information

Received Date: October 25, 2023
Revised Date: March 05, 2024
Accepted Date: March 12, 2024
Available Online: April 28, 2024

Abstract

HIGHLIGHTS
(1) The memory effects of Li and B in MC-ICP-MS are obvious, which results in a poor data reproducibility among different measurement batches.

(2) When the Li background is rinsed with 0.3% NaCl solution, the stability of Li isotope analysis is the best. The flexible blank deduction method is suitable for accurate determination of B isotopes.

(3) After using the suggested background cleaning method, the detection accuracy of international standards of Li and B isotopes can reach 0.2‰ and 0.3‰, respectively.

ABSTRACT

Lithium (Li) and boron (B) isotopes are excellent tracers in geological processes. In order to study and eliminate the memory effects of lithium and boron element in isotopic measurements using MC-ICP-MS, different background rinsing protocols were designed with reference to previous research. The δ⁷Li and δ¹¹B values of different types of reference materials were tested to evaluate the long-term reproducibility of the measurements using designated rinsing protocols for at least six months. The results show that using only 0.3% NaCl solution to clean the background for 60s can significantly reduce the lithium background signal and ensure the ⁷Li background signal is less than 5mV within 24h. The long-term external precision of δ⁷Li values for Alfa Li, an in-house standard, was 0.13‰ (2SD, n=73). Rinsing solutions, such as NAF and NH₃·H₂O could not significantly reduce the boron background of the instrument. However, the flexible blank subtracting method was used for precise determination of δ¹¹B values. The long-term external precision of δ¹¹B values for Alfa B was 0.19‰ (2SD, n=60). The average δ⁷Li and δ¹¹B values of different types of reference materials were tested using these rinsing protocols, and the results were well consistent with reported data, supporting the applicability of the conclusions. The BRIEF REPORT is available for this paper at http://www.ykcs.ac.cn/en/article/doi/10.15898/j.ykcs.202310260167.
- memory effect,
- lithium,
- boron,
- MC-ICP-MS,
- 0.3% NaCl solution,
- blank deduction
BRIEF REPORT
Significance: MC-ICP-MS is commonly used to determine the composition of lithium and boron isotopes. However, data quality is often limited due to significant memory effects caused by deposition or adhesion of Li and B into the instrument. The rinsing solutions, including NaCl solution for Li and ammonia or NaF solutions for B, were tried, to eliminate memory effects by previous work^{[12,16,27-28,32]}. However, the sensitivity and background of Li and B elements in different instruments are different, such as in Neptune or Nu MC-ICP-MS, the memory reduction method should be retested in a new instrument. In this paper attention to the Li and B memory effects and their reduction method in the isotopic measurements using Nu Sapphire MC-ICP-MS was given. The results show that using only 0.3% NaCl solution to clean the background can significantly reduce the lithium background signal, and ensure that the ⁷Li background value is less than 5mV within 24h. The flexible blank deduction technique can be used for precise determination of δ¹¹B values.

Methods: 0.1%(V/V) NaCl, 0.3% NaCl, 2.5% NaCl and 5% NaCl solutions were introduced for 1min to rinse the background of Li before a daily batch run. The background of Li after a normal 2% HNO₃ rinsing sequence and the internal precision (SE) of ⁷Li/⁶Li when testing 200ng/g Li sample solutions were recorded for several hours. For B isotopes measurement, water, 0.1% ammonia and 0.06mg/g NaF solutions were introduced for 1min or 2min to control the B memory effects. The background of B after a normal 2% HNO₃ rinsing sequence were recorded when testing an 80ng/g B sample solution. The blank subtraction method with different frequencies was also used to control the memory effects of B. The δ⁷Li and δ¹¹B values of standard materials and their external precisions (2SD) were calculated to ensure the accuracy and long-term stability of the measurements using a different memory reduction method.

Data and Results: The fluctuation of sensitivity of ⁷Li and internal precision (SE) of ⁷Li/⁶Li caused by Na were limited when 0.3% NaCl solution was introduced for 60s. In the meanwhile, the ⁷Li background signal decreased from 20mV to 4mV and remained a low level within 24h. Thus, a washing process included the following steps: 0.3% NaCl solution was introduced for 60s at intervals of about 24h, the background intensity determined (zero test) using 2% HNO₃ blank was subtracted before a daily batch run and 2% HNO₃ (2min) was used to rinse the background between each standard and samples. The δ⁷Li values of reference materials and their external precisions (2SD) were obtained in six months to ensure the accuracy and long-term stability of the data. The δ⁷Li values of IRMM-016, USTC-Li, Alfa Li and JG-2 with respect to L-SVEC were 0.12‰±0.07‰ (n=50), −19.3‰±0.12‰ (n=56), 13.7‰±0.13‰ (n=73), 0.13‰ ±0.11‰ (n=12), respectively.

　　The ¹¹B background signal could not be effectively reduced when the background rinsing solution was replaced with pure water, acidified NaF, ammonia and dilute nitric acid. To ensure the accuracy of the test, the background deduction method is flexibly selected, that is, each blank is deducted once between each standard and samples within the first 3h of the B isotope test sequence. Typical washing and testing process included the following steps: 120s 2% HNO₃ wash–60s wash solution uptake–30s 2% HNO₃ zero test–120s 2% HNO₃ wash–60s sample uptake–150s sample or standard measurement. The zero-testing process could be lessened to once every nine samples testing after 3h of the batch run. After six months of reference materials testing, the δ¹¹B values of ERM-AE121, ERM-AE122, Alfa B and NASS-7 were 19.78‰±0.31‰ (n=64), 39.54‰±0.33‰ (n=36), −4.66‰±0.19‰ (n=60) and 40.03‰±0.33‰ (n=35), respectively. The results were in good agreement with reported data, which indicates that excellent accuracy and precision can be achieved for Li and B isotope measurements using these designated rinsing protocols.

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References (35)

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