Polesello Stefano, Tartari Gabriele, Giacomotti Paola, Mosello Rosario, Cavalli Silvano
CNR-IRSA, via Mornera 25, I-20047 Brugherio, MI, Italy.
J Chromatogr A. 2006 Jun 16;1118(1):56-61. doi: 10.1016/j.chroma.2006.03.015. Epub 2006 Apr 18.
Studies of inorganic carbon cycle in natural waters provide important information on the biological productivity and buffer capacity. Determination of total inorganic carbon, alkalinity and dissolved carbon dioxide gives an indication of the balance between photosynthesis and respiration by biota, both within the water column and sediments, and carbon dioxide transfers from the water column to the atmosphere. There are few methods to measure and distinguish the different forms of inorganic carbon, but all require a measure or an indirect quantification of total inorganic carbon. A direct measurement of TIC in water is made possible by the introduction of electrolytic generated hydroxide eluent in ion chromatography which allows to detect a chromatographic peak for carbonate. The advantage of this method is that all the inorganic forms of carbon are converted in carbonate at eluent pH and can be detected as a single peak by conductivity detection. Repeatability of carbonate peak was evaluated at different levels from 0.02 to 6 mequiv.l(-1) both in high purity water and in real samples and ranged from 1 to 9%. The calibration curve was not linear and has to be fitted by a quadratic curve. Limit of detection was estimated to be 0.02 mequiv.l(-1). Accuracy has been estimated by comparing ion chromatography method with total inorganic carbon calculated from alkalinity and pH. The correlation between the two methods was good (R(2)=0.978, n=141). The IC method has been applied to different typologies of surface waters (alpine and subalpine lakes and rivers) characterised by different chemical characteristics (alkalinity from 0.05 to 2 mequiv.l(-1) and pH from 6.7 to 8.5) and low total organic carbon concentrations. This analytical method allowed to describe the distribution of TIC along the water column of two Italian deep lakes.
对天然水体中无机碳循环的研究为生物生产力和缓冲能力提供了重要信息。总无机碳、碱度和溶解二氧化碳的测定表明了水柱和沉积物中生物群的光合作用与呼吸作用之间的平衡，以及二氧化碳从水柱向大气的转移。测量和区分不同形式无机碳的方法很少，但都需要对总无机碳进行测量或间接定量。通过在离子色谱中引入电解产生的氢氧化物洗脱液，可以直接测量水中的总无机碳，从而检测到碳酸盐的色谱峰。该方法的优点是，在洗脱液pH值下，所有无机形式的碳都转化为碳酸盐，并可通过电导检测作为一个单峰进行检测。在高纯水和实际样品中，对0.02至6 mequiv.l(-1)不同水平的碳酸盐峰重复性进行了评估，范围为1%至9%。校准曲线不是线性的，必须用二次曲线拟合。检测限估计为0.02 mequiv.l(-1)。通过将离子色谱法与根据碱度和pH值计算的总无机碳进行比较，评估了准确度。两种方法之间的相关性良好（R(2)=0.978，n=141）。离子色谱法已应用于具有不同化学特性（碱度从0.05至2 mequiv.l(-1)，pH值从6.7至8.5）和低总有机碳浓度的不同类型地表水（高山和亚高山湖泊及河流）。这种分析方法能够描述意大利两个深湖水柱中总无机碳的分布情况。
