Since all TOC analyzers only actually measure total carbon, TOC analysis always requires some accounting for the inorganic carbon that is always present.  One analysis technique involves a two-stage process commonly referred to as TOC differential method. It measures the amount of inorganic carbon (IC) evolved from an acidified aliquot of a sample and also the amount of total carbon (TC) present in the sample. TOC is calculated by subtraction of the IC value from the TC of the sample.  Another method directly measures TOC in the sample by acidifying the sample to a pH value of two or less to release the  CO gas by decomposition of the carbonates and vent these gases to the air by a purge step.  The remaining non-purgeable organic carbon (NPOC) contained in the liquid aliquot is then oxidized releasing the CO gases.  These gases are then sent to the detector for measurement. This method is also referred to as the direct TOC method. A further variant employs acidification of the sample to evolve carbon dioxide and measuring it as inorganic carbon (IC), then oxidizing and measuring the remaining non-purgeable organic carbon (NPOC).  This is called TIC-NPOC analysis. TC oxidizes in a combustion chamber at 1000 degrees Celsius; if no supporting catalyst is used to allow full combustion at temperatures lower than 1000 degrees C; while the combustion chamber for IC heats only to 150 degrees Celsius. The reason for this is because inorganic is decomposed at lower temperatures than organic carbons. 
Whether the analysis of TOC is by TC-IC or NPOC methods, it may be broken into three main stages:
#Acidification
#Oxidation
#Detection and Quantification