Application of an Isotope Binary Mixing Model for Determination of Precise Mercury Isotopic Composition in Samples with Low Mercury Concentration

Abstract

An isotope binary mixing model was applied for high precision measurement of mercury isotope ratios in samples with low mercury concentrations by multicollector inductively coupled plasma mass spectrometry (MC-ICPMS). Standard addition was used to evaluate the precision and accuracy of the isotope composition calculations resulting from the isotope binary mixing model. A high, steady 202 Hg signal of approximately 2.13 V was achieved, with the mercury concentration reaching 3 ng/mL. The isotopic composition of three standards (NIST SRM 1646a; NIST SRM 1575a; BCR 482) and natural samples were precisely determined. The standards and natural samples were diluted to low mercury concentrations (low to 0.90 ng/mL) and mixed with standard solutions (NIST SRM 3133) with high mercury concentrations (50 ng/mL); the isotopic compositions of low mercury concentration samples were calculated using an isotope binary mixing model after the isotopic compositions of the mixing solutions were measured. The results showed that the uncertainty of the calculated mercury isotopic compositions was in an acceptable range and the calculation isotope data were in good agreement with direct measurements. Our method allows the precise determination of mercury isotope composition in mercury solutions of concentrations (0.90 ng/mL) below the detection limit of the current system (3.00 ng/mL).

Double Spike-Standard Addition Technique and Its Application in Measuring Isotopes

“…This method refers to the addition of high-purity standard material with known concentration to the sample, which can effectively reduce the blank and matrix effect. − Measurements calibrated by SA have greatly improved accuracy and precision . In recent years, attempts have also introduced SA to isotope measurement. − The SA method is primarily applied to check whether the isotope ratios are influenced by matrix effects, spectral interferences, and/or isotope fractionation during column chemistry. − At this stage, SA is still only evaluated to verify the accuracy and precision of isotope data. Recently, Huang et al combined SA and SSB to analyze Hg isotopic compositions of natural samples.…”

“…In recent years, attempts have also introduced SA to isotope measurement. − The SA method is primarily applied to check whether the isotope ratios are influenced by matrix effects, spectral interferences, and/or isotope fractionation during column chemistry. − At this stage, SA is still only evaluated to verify the accuracy and precision of isotope data. Recently, Huang et al combined SA and SSB to analyze Hg isotopic compositions of natural samples. The uncertainty of their method mainly comes from two parameters: the isotopic composition of the sample-standard mixture and the relative proportions of sample and standard.…”

“…Since the proportion of sample and standard is difficult to measure precisely, the data quality did not exceed that of direct SSB. For example, the actual precision (2-standard deviation (2SD)) of the sample fraction is 2.5–3% using direct SSB. , In that way, the estimated uncertainty of Hg isotopes should be commonly greater than 0.14‰ . Although multipoint correction is carried out by applying the isotope binary mixing model, the precision does not exceed that of traditional analytical methods, which restricts the application of the SA method in isotope analysis.…”

Isotopic measurements using ICP-MS: a tutorial review

“…A method for the measurement of mercury isotope ratios at low concentration levels has been published. 118 However, the measurement of compound-specic isotopic analysis of inorganic mercury and methylmercury is still in its infancy. 119 5.2.4 Fe, Cu and Zn isotope ratios for medical purposes.…”

Atomic spectrometry update: review of advances in atomic spectrometry and related techniques

“…Huang et al 134 used a binary mixing technique to determine Hg IRs in samples with <1 ng mL −1 Hg. This was tested by the standard addition of the CRM NIST SRM3133 to natural samples and extrapolation from the measured mixture ratio to the natural ratio.…”