Overview
ISO 14595:2023 - "Microbeam analysis - Electron probe microanalysis - Guidelines for the specification of certified reference materials (CRMs)" - provides guidance for specifying and testing single-phase certified reference materials (CRMs) used in electron probe microanalysis (EPMA). The third edition (2023) updates recommendations on heterogeneity assessment, stability under electron bombardment, analytical methods, specimen preparation, packaging, and certificate contents. The standard supplements ISO 17034 (producers of CRMs must also comply with ISO 17034; in case of conflict ISO 17034 takes precedence). It does not cover organic or biological materials.
Key topics and technical requirements
- Selection and preliminary inspection: choose dense, single-phase material free of inclusions; document origin/preparation for synthetic or mineral RMs. Mounts should provide multiple flat areas (~20 µm or larger) for point analysis.
- Heterogeneity assessment:
- Use a 1 µm point beam for micrometre-scale heterogeneity; a defocused beam (~5 µm) may be used for beam-sensitive specimens (then CRM is limited to defocused-beam use).
- Wavelength-dispersive spectroscopy (WDS) is preferred for heterogeneity tests because of higher count rates; energy-dispersive spectroscopy (EDS) is acceptable when WDS is unsuitable.
- Recommended excitation voltage should give adequate overvoltage (typically ≥1.5× the critical excitation potential).
- Guidance on sample size: test a statistically representative number of specimens (examples range from small sets of 5–20 to larger populations); consult a statistician for study design.
- Statistical evaluation procedures (including spreadsheet instructions in Annex A) and criteria for certification are provided.
- Stability: evaluate both long-term chemical stability (storage) and stability under electron bombardment (X-ray intensity changes).
- Chemical composition determination and classification: methods selection, classification schemes for CRMs (Annex B), and cases where EPMA-only testing is appropriate.
- Specimen handling: polishing, coating, packaging, transport, storage, and procedures for repolishing/recoating.
- Certification information: required contents of CRM certificates and example certificate (Annex C).
Practical applications and who uses it
ISO 14595:2023 is essential for:
- CRM producers who need to specify and certify reference materials for EPMA calibration and quality assurance.
- Materials scientists, geologists, metallurgists, ceramists, and mineralogists performing microbeam analysis.
- Accreditation bodies, metrology laboratories, and inter-laboratory comparison organizers to ensure traceable, comparable EPMA results.
- EPMA laboratories and instrument manufacturers seeking guidance on CRM selection, use, and limitations (e.g., beam sensitivity or required beam geometry).
Related standards
- ISO 17034 - General requirements for the competence of reference material producers (takes precedence in conflicts).
- ISO/TC 202 publications on microbeam analysis and other EPMA-related guidance (see ISO catalogue for related documents).
Keywords: ISO 14595:2023, EPMA, electron probe microanalysis, certified reference materials, CRMs, microbeam analysis, heterogeneity, WDS, EDS, CRM certification.
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