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

Area of Science:

• Geochemistry
• Analytical Chemistry
• Isotope Geochemistry

Background:

• The Double Spike (DS) method is widely used for stable isotope ratio determination.
• High-precision isotope analysis of ultra-trace elements is challenging due to signal-to-noise limitations and measurement precision issues with the DS method.

Purpose of the Study:

• To introduce and validate the Double Spike-Standard Addition (DSSA) technique for improved isotope measurements of ultra-trace elements.
• To address the limitations of traditional DS methods in analyzing trace elements.

Main Methods:

• Developed theoretical equations and an error propagation model (EPM) based on the U-shaped relationship between DS measurement uncertainty and spike/sample ratio.
• Mixed samples with a spiked secondary standard solution to achieve optimal spike/sample ratios within a recommended range (f_spl = 0.15-0.5).
• Utilized a standard DS data reduction routine and isotope binary mixing model to determine sample abundances and isotope ratios.

Main Results:

• Verified the accuracy and precision of the DSSA approach using cadmium and molybdenum isotopes at trace levels (5 ng).
• Reduced sample size for isotope analysis by 5-6 times compared to traditional DS methods without compromising measurement precision.
• Demonstrated the applicability of DSSA for over 33 elements, particularly ultra-trace elements like platinum group and rare earth elements.

Conclusions:

• The DSSA technique offers a significant advancement for precise isotope analysis of ultra-trace elements.
• This method overcomes key limitations of traditional DS measurements, enabling analysis with smaller sample sizes.
• DSSA has broad applicability across various elements, especially those found at ultra-trace concentrations in natural samples.