Collision and reaction cell (CRC)

A pressurised cell between the skimmer and the quadrupole, charged with helium for kinetic-energy-discrimination collision mode or with hydrogen, ammonia or oxygen for chemical-resolution mode. Helium knocks larger polyatomics off course; reactive gases convert or mass-shift the interference. The CRC is what made quadrupole ICP-MS routine for arsenic, selenium and chromium in real matrices.