ISO 16666:2025

Overview - ISO 16666:2025 (TXRF)

ISO 16666:2025, "Surface chemical analysis - Total reflection X‑ray fluorescence - Principles and general requirements", defines the physical principles, instrument characteristics and general procedures for total reflection X‑ray fluorescence (TXRF) spectrometers. The standard covers instrument design and alignment, measurement geometry (fixed glancing angle below the critical angle), calibration and method development, quality control, spectra processing, and verification of quantitative TXRF measurements. It is focused on TXRF conditions that exploit enhanced excitation intensity and reduced background; it does not apply to grazing‑incidence setups (GIXRF).

Key technical topics and requirements

• Physical principles: Geometry of TXRF, beam projection, X‑ray standing waves (XSW) and fluorescence intensity under total reflection conditions.
• Instrumental requirements: Descriptions of typical TXRF setups, beam conditioning and guidance, measurement angles, reflectors (sample carriers), reflector alignment, detectors (e.g., SDDs), sample station and control unit.
• Calibration & quality control: Procedures for angle inspection, energy calibration, calibration of element sensitivities, inspection of excitation and detection performance, and round‑robin verification approaches.
• Spectra analysis & reporting: Spectral processing, background/peak correction, deconvolution and reporting conventions for TXRF results.
• Quantitative methods: Qualitative and quantitative analysis workflows including element‑specific sensitivity methods (internal standard addition), preparation and verification of quantitative measurements, and traceability considerations.
• Practical considerations: Sample types, measurement limits inherent to TXRF, and how to maintain reproducibility and accuracy in routine and research environments.

Practical applications and who uses this standard

ISO 16666:2025 is practical for organizations and professionals who perform or support surface and trace element analysis using TXRF:

• Analytical laboratories performing trace element and surface contamination analysis.
• Semiconductor and microelectronics fabs for wafer contamination screening.
• Environmental and biological testing labs using TXRF for low‑mass or thin‑film analyses (complementary standards address water and specific substrates).
• Instrument manufacturers and system integrators designing TXRF spectrometers and components (reflectors, detectors, beam optics).
• Metrology institutes and quality managers implementing calibration, uncertainty evaluation and traceability for TXRF methods.

Related standards

• ISO 18115‑1 (vocabulary for surface chemical analysis)
• ISO 20289 (TXRF of water)
• ISO 14706, ISO 17331 (application‑specific TXRF standards for silicon wafers)
• JCGM 100 (GUM - Guide to the expression of uncertainty in measurement)

ISO 16666:2025 is essential reading for ensuring robust, reproducible TXRF measurements and for establishing best practices in instrumentation, calibration and method verification for high‑sensitivity surface chemical analysis.