This document describes a validation protocol for sampling systems used to collect samples of hydrogen at an HRS for subsequent purity analysis following for example EN 17124:2022 or ISO 14687:2025 standards. It is mostly based on knowledge gathered from experiments performed during the MetroHyVe2 and MetHyTrucks projects. However, full validation of hydrogen sampling systems remains challenging due to the complexity of replicating real refuelling conditions and the difficulty of assessing trace contaminants with high confidence. A combined strategy—integrating field validation, laboratory testing, and equivalence assessment—therefore represents the most robust and pragmatic approach.