An attachment for an Eppendorf tube that allows a Mylar or Prolene film to be stretched across it, enabling XRF measurements without the need to transfer the sample. The adapter consists of two parts: the main insert is placed into the Eppendorf tube, a film is laid over it, and a retaining ring is used to tension and secure the film. The design can be manufactured using an filament 3D printer, although a resin printer is recommended for better precision and surface quality.