Technical Note: Precise quantitative measurements of total dissolved inorganic carbon from small amounts of seawater using a gas chromatographic system

摘要

Total dissolved inorganic carbon (C_T) is one of the mostfrequently measured parameters used to calculate the partial pressure ofcarbon dioxide in seawater. Its determination has become increasinglyimportant because of the rising interest in the biological effects of oceanacidification. Coulometric and infrared detection methods are currentlyfavored in order to precisely quantify C_T. These methodshowever are not sufficiently validated for C_T measurements ofbiological experiments manipulating seawater carbonate chemistry with anextended C_T measurement range(~1250–2400 μmol kg–1) compared to natural open oceanseawater (~1950–2200 μmol kg?1). The requirement oftotal sample amounts between 0.1–1 L seawater in the coulometric- andinfrared detection methods potentially exclude their use for experimentsworking with much smaller volumes. Additionally, precise C_Tanalytics become difficult with high amounts of biomass (e.g., phytoplanktoncultures) or even impossible in the presence of planktonic calcifiers withoutsample pre-filtration. Filtration however, can alter C_Tconcentration through gas exchange induced by high pressure. Addressing theseproblems, we present precise quantification of C_T using a small,basic and inexpensive gas chromatograph as a C_T analyzer. Ourtechnique is able to provide a repeatability of±3.1 μmol kg?1, given by the pooled standard deviationover a C_T range typically applied in acidification experiments.200 μL of sample is required to perform the actual C_Tmeasurement. The total sample amount needed is 12 mL. Moreover, we show thatsample filtration is applicable with only minor alteration of theC_T. The method is simple, reliable and with low cumulativematerial costs. Hence, it is potentially attractive for all researchersexperimentally manipulating the seawater carbonate system.