The document provides the physical principles and specifies instrumental requirements for total reflection X‑ray fluorescence analysis (TXRF) spectrometers. This practice includes sampling issues such as the selection of storage ves els, transportation, and sub-sampling. Treatment, assembly, and handling of. 5. thus x-rays, If the tube Is not in the machine. 3 This instrument is equipped with a fail-safe x-ray warning light, shutter open. This Code of Practice covers information relating to sampling, calibration and validation of X-ray fluorescence instruments for elemental analysis, including all kinds of wavelength dispersive (WDXRF) and energy dispersive (EDXRF) techniques.