These standards are used to optimize liquid scintillation counter settings and to check long term stability of the instrument. Each standard contains PPO/Dimethyl POPOP in scintillation grade toluene, is argon purged and is flame sealed in a borosilicate ampoule. Each standard has a cap designed for high reflectivity and ease of handling. Unquenched LSC standards are available in two sizes: standard size for use with instruments using standard 20 mL vials and Pico standards for small vial systems.