ABSTRACT

Ethanol contamination recently identified in Ryugu samples was traced to fluoroelastomer O-rings used in the Facility-to-Facility Transfer Container (FFTC). To eliminate this contamination source, the O-ring preparation procedure was revised by minimizing ultrasonic cleaning with high-purity ethanol, introducing vacuum baking at 150°C, and storing O-rings under vacuum or dry nitrogen until use. Thermal desorption–comprehensive two-dimensional gas chromatography–time-of-flight mass spectrometry showed that residual ethanol in the O-rings decreased by more than four orders of magnitude to <1 μg per ring compared to the conventional cleaning procedure. Transport experiments further demonstrated that samples carried in the improved FFTC exhibited ethanol, acetaldehyde, and acetone levels comparable to those transported in an O-ring-free metal-seal container. The revised protocol provides an effective and practical approach for contamination-controlled transport of returned extraterrestrial samples.