Classification of microheterogeneity in solid samples using microXRF.

Area of Science:

• Materials Science
• Analytical Chemistry
• Geochemistry

Background:

• Reference materials are crucial for accurate analytical measurements.
• Traditional methods often require larger sample masses (e.g., 100 mg by NIST).
• Elemental heterogeneity, or "nugget effects," can impact representativeness in small samples.

Purpose of the Study:

• To investigate elemental heterogeneity in reference materials using micro X-ray fluorescence (microXRF).
• To assess the feasibility of using microXRF for sub-milligram sample analysis.
• To develop a method for determining minimum sample mass to avoid nugget effects.

Main Methods:

• Nondestructive elemental mapping using micro X-ray fluorescence (microXRF).
• Application of multivariate analysis, specifically principal component analysis (PCA), to elemental maps.
• Iterative averaging of X-ray map data to simulate increasing sample masses and assess nugget effects.

Main Results:

• PCA effectively identifies elemental heterogeneity and "nugget effects" in reference materials (SRM 2702, SRM 2703).
• MicroXRF analysis is feasible for sample masses significantly below 100 mg.
• A method was proposed to calculate minimum sample mass, demonstrating 370 microg is sufficient for SRM 1577c without measurable nugget effects.

Conclusions:

• MicroXRF combined with PCA is a powerful tool for characterizing elemental heterogeneity in small sample masses.
• This approach allows for reduced sample requirements in reference material analysis.
• The proposed method provides a quantitative basis for determining minimum sample mass, enhancing analytical reliability.