Characterization of a new candidate isotopic reference material for natural Pb using primary measurement method

Area of Science:

• Analytical Chemistry
• Geochemistry
• Isotope Ratio Mass Spectrometry

Background:

• Accurate lead isotope ratio measurements are crucial for various scientific applications, including geochronology and environmental studies.
• Existing isotopic standards may have limitations in precision or availability.
• Development of novel, high-precision lead isotopic standards is essential for advancing analytical capabilities.

Purpose of the Study:

• To develop a lead isotopic standard solution with natural abundance using a bracketing method with a 208Pb-204Pb double spike solution.
• To accurately determine the amount-of-substance ratio of 208Pb:204Pb in the double spike solution.
• To measure lead isotope ratios in a candidate standard solution with high precision and compare it with existing standards.

Main Methods:

• Preparation of a 208Pb-204Pb double spike solution by mixing enriched 208Pb and 204Pb solutions.
• Accurate determination of the 208Pb:204Pb ratio using EDTA titrimetry, a primary measurement method.
• Quantification of metal impurities and minor lead isotopes using ICP-SF-MS.
• Measurement of lead isotope ratios in the candidate standard using a coupled bracketing method with the double spike solution and a thallium internal addition method in MC-ICP-MS.
• Validation of the method by analyzing NIST SRM 981.

Main Results:

• The amount-of-substance ratio of 208Pb:204Pb in the double spike solution was determined as 0.961959 ± 0.000056.
• The developed method achieved significantly higher precision for lead isotope ratios (e.g., 208Pb:204Pb, 207Pb:204Pb, 206Pb:204Pb, 208Pb:206Pb, 207Pb:206Pb) compared to NIST SRM 981.
• Measured lead isotope ratios in NIST SRM 981 using the developed method showed good agreement with certified values, validating the technique.

Conclusions:

• The developed 208Pb-204Pb double spike bracketing method coupled with thallium internal addition provides a highly precise way to measure lead isotope ratios.
• This new method offers superior precision over conventional standards like NIST SRM 981, particularly for ratios involving minor isotopes.
• The developed lead isotopic standard solution and measurement technique are reliable for accurate isotopic analysis in various scientific fields.