Abstract: A method and apparatus for the measurement of the total organic carbon (TOC) content of a liquid is shown. The inorganic carbon in the liquid is converted into carbon dioxide and removed from it. At the same time, oxygen is added to the liquid. The liquid is then exposed to ultraviolet radiation and the organic carbon thereby oxidized. This oxidized carbon, in the form of carbon dioxide, is allowed to migrate across a gas-permeable, liquid-impermeable membrane directly into a measurement chamber, where its absorption of radiation is measured to determine its concentration.