Online determination of mercury isotopic compositions at ultratrace levels by automated purge and trap coupled with multicollector inductively coupled plasma-mass spectrometry

• Published in: Journal of analytical atomic spectrometry 2022-11, Vol.37 (11), p.248-2489
• Main Authors: Yang, Lin, Yu, Ben, Liu, Hongwei, Ji, Xiaomeng, Xiao, Cailing, Liang, Yong, Hu, Ligang, Yin, Yongguang, Shi, Jianbo, Jiang, Guibin
• Format: Article
• Language: English
• Subjects: Automation; Composition; Inductively coupled plasma mass spectrometry; Isotopes; Mass spectrometry; Optimization; Scientific imaging; Spectroscopy
• ISSN: 0267-9477; 1364-5544
• DOI: 10.1039/d2ja00148a

Characterizing natural mercury (Hg) isotopic compositions in geological and environmental matrices provides a better understanding of the biogeochemical cycles of Hg. However, preconcentration is indispensable for the determination of samples with low Hg contents ( e.g. , ng L −1 levels), which is time-consuming and requires a lot of manpower and materials. Herein, a sensitive method for the online determination of Hg isotopic compositions by automated purge & trap (P&T) coupled with multicollector inductively coupled plasma-mass spectrometry (MC-ICPMS) was developed. Rapid Hg isotopic analysis was realized in 15 min (single sample-standard bracketing procedure) with a sample consumption of 25 mL per measurement. The optimization of the P&T module and MC-ICPMS was conducted to obtain a high sensitivity for Hg isotopic determination ( 202 Hg max intensity over 10 V for 40 ng L −1 Hg solution). Strategic signal acquisition and data treatment using the linear regression slope without time-lag correction were applied. Accurate isotopic compositions in a referenced standard solution at 8 ng L −1 (NIST 3177, δ 202 Hg −0.55 ± 0.29‰, Δ 199 Hg −0.02 ± 0.23‰, Δ 200 Hg 0.01 ± 0.19‰, Δ 201 Hg −0.02 ± 0.16‰, 2SD, and N = 31) and certified reference materials (CRMs) at 40 ng L −1 were obtained (NRC DORM-4, δ 202 Hg 0.45 ± 0.14‰, Δ 199 Hg 1.73 ± 0.16‰, Δ 200 Hg 0.06 ± 0.08‰, Δ 201 Hg 1.42 ± 0.13‰, 2SD, N = 13; NIST 1632e, δ 202 Hg −2.22 ± 0.19‰, Δ 199 Hg −0.02 ± 0.07‰, Δ 200 Hg 0.00 ± 0.07‰, Δ 201 Hg −0.01 ± 0.09‰, 2SD, and N = 20). The measuring concentration of this proposed method has decreased from μg L −1 to ng L −1 levels compared to CV introduction. The sample size and analytical time are 2-3 orders of magnitude lower compared to offline preconcentration methods (several hours to process several to dozens of liters). This proposed method can be used for the analysis of Hg isotopic compositions in solution samples with low Hg concentrations including natural aquatic samples. This study reports a sensitive online method for Hg isotope analysis at ultratrace levels by automated P&T-MC-ICPMS.