Total dissolved inorganic carbon (<i>C</i>_T) is one of the most frequently measured parameters used to calculate the partial pressure of carbon dioxide in seawater. Its determination has become increasingly important because of the rising interest in the biological effects of ocean acidification. Coulometric and infrared detection methods are currently favored in order to precisely quantify <i>C</i>_T. These methods however are not sufficiently validated for <i>C</i>_T measurements of biological experiments manipulating seawater carbonate chemistry with an extended <i>C</i>_T measurement range (~1250–2400 μmol kg^&ndash;1) compared to natural open ocean seawater (~1950–2200 μmol kg⁻¹). The requirement of total sample amounts between 0.1–1 L seawater in the coulometric- and infrared detection methods potentially exclude their use for experiments working with much smaller volumes. Additionally, precise <i>C</i>_T analytics become difficult with high amounts of biomass (e.g., phytoplankton cultures) or even impossible in the presence of planktonic calcifiers without sample pre-filtration. Filtration however, can alter <i>C</i>_T concentration through gas exchange induced by high pressure. Addressing these problems, we present precise quantification of <i>C</i>_T using a small, basic and inexpensive gas chromatograph as a <i>C</i>_T analyzer. Our technique is able to provide a repeatability of ±3.1 μmol kg⁻¹, given by the pooled standard deviation over a <i>C</i>_T range typically applied in acidification experiments. 200 μL of sample is required to perform the actual <i>C</i>_T measurement. The total sample amount needed is 12 mL. Moreover, we show that sample filtration is applicable with only minor alteration of the <i>C</i>_T. The method is simple, reliable and with low cumulative material costs. Hence, it is potentially attractive for all researchers experimentally manipulating the seawater carbonate system.